It is all subjective, but I would say that a public place is better (as I have previously answered to a similar question ).
Most bike thefts are opportunistic; unless you've got an especially desirable bike the theft is not about your bike, it's about stealing any bike.
So the key is to reducing the opportunity to steal your bike: as you point out, reducing the amount of time to work on the lock(s) make it less desirable and more identifiable (dirt, scuffs, mods) give alternatives - parking next to a shiny newer more expensive looking one with a poorer lock I would also say to try to use a public bike rack - then you've also got a chance that a fellow cyclist would interrupt or at least deter a thief.
Several times I've seen someone suspicious loitering around a bike rack when locking/unlocking my bike and I've taken longer about it so as to make them feel uncomfortable and move on.
I don't want my bike nicked and spending a few minutes to maybe slightly protect someone else's makes me feel like a good citizen.
bicycles.stackexchange.com/users/425/Unsliced
In the end it might matter more WHO is around the rack (policemen, guards, janitors, public workers, parking lot workers, hot-dog stand owners, etc.)
than HOW MANY people.
I'd rather, when available, leave my bike under one lonely ever-present alert pair of eyes than in a crowd of anonymous passers-by.
bicycles.stackexchange.com/users/2355/heltonbiker
I've seen videos showing people stealing bikes amidst a crowd of onlookers while no one intervenes.
Locking in a crowded place isn't necessarily going to save your bike.
On the other hand, lots of bikes are stolen from locked garages.
I'm not aware of any statistics about what storage method is safer.
I've never had a bike stolen, but from what I've heard in my social circles, most people's bikes have been stolen while they had locked it up during an outing in the evening, or overnight.
It's always "when I left the bar it was gone," or "in the morning it was gone."
For this reason, I think it's safest to bring your bike into your home overnight.
bicycles.stackexchange.com/users/2824/Darth Egregious
I would say a quieter place is better.
less people see it, less likely a thief see's it also.
I have had a bike stolen, well a bike wheel actually, stolen from outside my offices - in front of a security guard and cctv camera (both useless it would seem).
bicycles.stackexchange.com/users/484/NimChimpsky
Is this link any use?
This ex-bike-thief basically says to lock your bike the busier the better.
http://www.guardian.co.uk/environment/green-living-blog/2010/sep/13/bike-thief-stolen-tips
As I have posted on here previously, I think if someone decides they are going to go out of their way to steal your bike
, I'm not sure you'll be able to stop them.
But presumably your bike is/will be insured?
If so, read the policy thoroughly and make sure you comply with the minimum specified security requirements.
At least if it does get stolen you'll have some compensation.
In my case the policy covers the grade of lock I need to use (in the UK
there is a standard called "Sold Secure", its arguable whether locks that conform to this standard are better than locks that don't, but it is a standard that appears to keep the insurance companies happy), what I lock the bike to, and how long I can lock it for.
EDIT: If the link above was useful, there's a further excellent link from the Guardian - How to protect your bike from being stripped for parts
bicycles.stackexchange.com/users/4808/PeteH
Its really not sure, both way have their own disadvantages.
I will say never park your bike anywhere, where there is a chance of you losing its sight, whether busy or quite place.
When you have to be permanently out for several hours, then Find a good secured parking spot to park your bikes.
There should be a guard around or someone who is responsible.
make sure he knows you have parked a bike.
Or, you can also ask him to keep an eye on the bike (depending on the nature of the person)
If its possible, make irregular visits to the parking spot.
Confusing the thief.
Complete your work and rush to your bike :) At my city, I park around a firm thing.
Whether poles, or railing, to increase the difficulty ( but its not allowed everywhere, so not so helpful ).
bicycles.stackexchange.com/users/847/Starx
Hal Ruzal, a bike security expert, has a series of videos on YouTube , some of which are done in conjunction with the police.
In one he answers just this very question.
His answer is not what you may think and does not match the current top answer here.
He says it is much better to lock it in a quiet area.
This is because the thieves are more edgy in terms of being seen or heard.
In a busy area they are not noticed and the noises and things they do blend in with all else that is going on.
He has spoken to thieves and knows how they work / think.
He often grades bikes based on how well they are locked.
If you can keep your eye on it then that is a different matter of course.
And of course it must be locked to something secure which may also determine where you lock it.
I would also add that locking it next to other bikes does not work as some answers suggest.
As the thief blends in.
You look and think he is just unlocking his bike next to yours -
but he is after your bike!
I once came out of an office where I locked my bike next to others to find a guy suddenly jump.
I swore
I saw him trying to unlock my bike and move away.
He seemed to then pretend he was unlocking the bike next to mine!
I was not sure
so just left it as my lock and bike were not damaged.
He may have been trying to pick the lock.
But it shows how they blend in this way.
bicycles.stackexchange.com/users/13954/Andrew Norris
When I lock my bicycle I try to lock it on quiet spots, usually on street racks situated on secondary streets.  I think it will be less visible so it  will attract less looks. On the other hand, if a thief wants to steal it, he will have more time to act before someone spots him.  Is it better to lock the bicycle in crowded or quiet locations?
Lock my bicycle on busy or quiet places?
bicycles.stackexchange.com
<security><lock><city>
bicycles.stackexchange.com/questions/12428
bicycles.stackexchange.com/users/3304/yeforriak
There is little consensus on whether your bike is more likely to get stolen if parked in a crowded place or a quiet street and there do not seem to be any official figures on the matter. Both places have advantages and disadvantages. However, the nicer your bike is, the more likely it is to get stolen, it is believed. Thus, parking next to a better-looking  bike may be the best answer. Apparently, most bikes are stolen in the evening or at night so it is probably better to keep your bike inside at that time. It is difficult to say objectively which is better, but thieves tend to be opportunistic and may be able to use the anonymity of crowds as well as the isolation of a quieter place. Leaving it during an outing or overnight seems to be more risky. Most thieves are not targeting individual bikes, so making a bike more difficult to steal and less appealing can help. Crowds are unlikely to stop a thief, especially when moving staying for a short time, but a security guard or vendor might be more aware of their surroundings and more willing to intervene.
It is difficult to say objectively which is better, but thieves tend to be opportunistic and may be able to use the anonymity of crowds as well as the isolation of a quieter place. Leaving it during an outing or overnight seems to be more risky. Most thieves are not targeting individual bikes, so making a bike more difficult to steal and less appealing can help. Crowds are unlikely to stop a thief, especially when moving staying for a short time, but a security guard or vendor might be more aware of their surroundings and more willing to intervene.