Ultimately it's a trade-off between a wider range of gears and bigger jumps between those gears.
There will always be uphills that are too steep for your lowest gear and downhills where you spin out.
If you try to fix both problems with a wider range cassette (your triple already has a great range)
you may find that you're never quite in the "right" gear for all of the in-between situations.
I'm using a 11-32 cassette on my road bike (with a MTB derailleur for more capacity).
I have plenty of climbing gears but rarely use the small cogs since I spin at around 90rpm.
Like the Bay Area, there are a lot of hill around here.
But I find the jumps between gears too big (either spins too easily or too hard) so am looking for a narrower range cassette.
If you want just a bit more range for climbing, you'll need to jump up to at least a 28-tooth large cog
(you'll barely notice the difference going from 26 to 27) which might require a long-cage derailleur.
On the high end, a 12-tooth cog will be a noticeable difference over your 13.
Since you're used to a compact range you probably don't want to go with a much bigger cassette.
Sheldon Brown has a great gearing calculator that you can play with to see what different combinations will give you.
bicycles.stackexchange.com/users/157/darkcanuck
A 12-27 cassette would give you a slightly wider spread of gears.
Depending on your drivetrain you might be able to fit a 11-32 MTB cassette, though you'll probably need an MTB rear derailleur too.
The jumps between ratios on wider cassettes can be annoying, though.
bicycles.stackexchange.com/users/272/markdrayton
It certainly sounds like you should look at going to a wider range of gears.
Your triple on the front already seems like a pretty wide range, and unlikely to easily get a wider range up there, so I'm thinking you'd mostly be looking at a wider range on the cassette.
The downside of widening your gear range will (generally) be that you'd get less fine tuning of gears inside your range.
You should definitely pay attention to the actual gear ratios.
Some careful selection (work out all your current gears and figure out what the new gears would be) could help a lot.
Right now your low end is basically 1:1 and your high end is 4.1:1.
A smallest sprocket of 11 instead of 13 (without changing from a 53) would get you to 4.8:1 for your highest gear, which is about an 18% improvement and could easily be enough to get you the higher-end range it sounds like you need.
Much more low end than that might require replacing the rear derailer,
but I've seen 11-34, etc, which would get your lowest gear down to 0.8:1.
Usually those have a specific "granny" gear on the back that's a big jump, which could still leave you with plenty of fine tuning in the rest of your gear range.
bicycles.stackexchange.com/users/76/freiheit
Another option to consider is a “ bottom bracket gear ”, these do not come cheap but can increase your gear range by a factor of 2.5.
bicycles.stackexchange.com/users/132/Ian
I highly recommend getting a compact crank (50/34) since for the vast majority of mere mortals a 53/39 crank is too much gearing.
It's a relatively cheap upgrade (about $300).
I pair mine with a 12-27 9 speed cassette.
Around here in Seattle, I find that there really aren't any hills I can't climb with the 34x27.
For my weight (160lbs) that lets me climb pretty much anything around here, including some hills with a 17%+ grade.
However, I'm finding that I could really use some additional gears so that I can pedal an optimal cadence.
I suspect a 12-13-14-15-16-17-19-21-23-25 is in my future someday when I can do 5 min climbs at 300W+.
But that's a really expensive upgrade though since that involves swapping out my 9spd drivetrain for a 10spd one.
That will happen when I get a new bike ...
bicycles.stackexchange.com/users/295/John Lam
Since you have a triple you already have about as wide a range as you can get on the front (for practical purposes).
Before changing the rear you would want to make sure your derailleurs can handle the increased range of teeth.
If you go to the manufacturers' websites (I'm guessing....
Shimano?)
you can look up the tooth capacity of those components.
If they will handle it, then you might be able to get a wider rear cassette that helps you.
bicycles.stackexchange.com/users/328/Jay
If you like to visit very steep climb, I suggest using 50/34 for chainring and 12/27 10 speed12,13,14,15,16,17,19,21,24,27 for your sprocket, or 11-28 includes - 11,12,13,14,15,17,19,21,24,2827 or 28 is very usefull if you climb more than 25% grade...
But if you have a strong power output 53/39 chainring with 12-25 includes - 12,13,14,15,16,17,19,21,23,25 should be sufficient...
I did 20% with 39/25....
so every one is unique for this sprocket/chainring selection, depends on your leg :)
bicycles.stackexchange.com/users/3189/Rick Ant
My road bike currently has a 27/39/53 crankset and a 13-26 cassette, both of which need to be replaced.  I occasionally find myself in both extremes—while heading up the very steep hills of the Bay Area the lowest gearing sometimes isn't enough and on much of a downhill grade my legs can't keep up in the highest.  Is it worth going to a wider range on the front or rear?
What range of sprockets is useful in a road bike cassette?
bicycles.stackexchange.com
<gears><cassette><crankset>
bicycles.stackexchange.com/questions/700
bicycles.stackexchange.com/users/17/Drew Stephens
A compact crank (50/34) is highly recommended since for the vast majority of people a 53/39 crank is too much gearing. The downside of widening your gear range will (generally) be that you'd get less fine tuning of gears inside your range. Another option to consider is a “ bottom bracket gear ”, these do not come cheap but can increase your gear range by a factor of 2.5.  There seem to arguments for a wider range both on the bike's front and on the rear. Most notably, a wider cassette would require a rear derailleur, and would also entail more complicated gearing. A good, if expensive, solution might be a bottom bracket gear.
There seem to arguments for a wider range both on the bike's front and on the rear. Most notably, a wider cassette would require a rear derailleur, and would also entail more complicated gearing. A good, if expensive, solution might be a bottom bracket gear.