Hello [MENTION=251284]louye2[/MENTION] - Welcome! You've got a lot of choices and it will depend on many things. I'm somewhat new to the technicalities of gearing and such, but I'll throw out some questions and ideas.

Are you happy with the current setup in regard to your ability to go up hills (large cog) and your desire/ability to go really fast (small cog)? When you have 7 choices within a small range like you currently have (road cassette), there are smaller differences between each cog/gear, so as you shift you don't notice the changes as much. It's about keeping your cadence at an even rate, which road cyclists like. When you have 7 speeds within a wider range, there are usually larger jumps between each shift, especially as it nears the lower gears (bigger cogs). How often do you ride in your 11 cog? If not often, then I'd start with a 12 or 13 as my smallest cog.

I had this choice last spring and was trying to figure it out. I told the bike shop that my riding style doesn't have me in my high gear tearing down hills or straight always as fast as I can go, therefore they did not recomment I get a cassette with an 11 or 12 high gear - I'd never use it. However, I do have some hills I'd like to be able to go up with some help, but they're not super huge, so we didn't go with the 32 or 34 low gear, as I'd likely not need it for my type of riding. I like somewhat even spacing between shifts, but want more than 2 teeth difference between each cog - when I shift I at least want to be able to feel the difference. Anyway I think I went 12-30 or 13-28 or something in that range. I have a triple chain ring up front for reference.

Its also a good idea to buy a new chain with your cassette, as they wear together over time, so budget for that.

heres the bike in question:

Sorry the photos ended up in crazy positions. Not sure how that happened.