What can I expect after university (taking CompSci)?

Both are good. It's up to your own choice and interest.

I work in web development and really like it.

One of the biggest differences is, with desktop apps, you normally need to support multiple versions of code simultaneously. With hosted web apps, all of your users are running the same version software and updates happen automatically.

Web companies tend to have smaller teams, so you have more control as an individual developer, and the development cycle is shorter. At the same time, your product will have a worldwide audience, so the potential for growth is huge.

If you decide to work on desktop apps, I’d recommend writing native Mac OS X apps, using the Carbon and Cocoa frameworks. If you go the web app route, I’d recommend working in Rails or Django (Fluther is written mostly in Django). Either way, I can’t stress enough the importance of working with a framework you love.

I work in web development and it’s light-years from what I would have chosen or even what I tried to choose, and light-years away from what my undergraduate computer science education prepared me for. I wouldn’t say I hate it, but there’s a reason I leave work by 6 just about every night and spend my evenings doing fulfilling non-technical things.

I would advise this: go to a school where you aren’t locked into a computer science major. (This is also good advice because you’ll be much better educated and a much more attractive candidate if you have a second major or a minor in something else that interests you that isn’t technical.) Then, after your first year, get a summer internship doing something in the computer industry.

If you hate your internship, you will have found out what the computer industry is like in plenty of time to change your path. If you hate your classes but love your internship, you have something that will motivate you to get you through the next three years. And if you love your classes and love your internship, you’re in a very sweet spot.

Meanwhile – you’re 16. Try a bit of desktop development (such as with Cocoa or Carbon – the very same dev tools that Apple developers use come for free with OS X), and a bit of web development (with Python and Django, Perl and Catalyst or Mason, or Ruby on Rails). See which one you prefer—they’re very different, but the differences are largely apparent once you’ve produced functioning apps in either framework. Other than that, the rough differences are as sferik laid out.

you can expect to make more money, but you’ll gain weight. Also, you’ll lose your hair and those older women who you used to think were matronly will start looking like hot mamas.