I got my HTC Aria for free through Best Buy about a year and a half ago. It's a good phone, I've been mostly happy with it, but there are enough negative things about it that make me want to switch back to iOS (my previous iOS device was an ipod touch from two years ago).
1) I have spent money on iOS apps - not a lot, but I'm broke, so enough.
2) Quality of free apps in the app store sucks compared to iOS - the best solitaire game I can find for free doesn't have an undo button for the game I play the most. Other apps I enjoy using aren't available for the android.
3) Camera pictures are taken by pressing the optical joystick. Doing that jiggles the phone, of course, which ruins 99% of my pictures. No flash is also a major bummer
4) Not all apps can be run off the SD card. My stupid little Aria has only 512 megs of internal memory. I joined Weight Watchers in November, downloaded the app, only to find out it is required to run on internal memory, and takes up over 100 megs of space. Even with deleting everything I could I didn't have enough room to run my app
5) Random crashing of apps with weird error messages. Now, I've been a Linux sysadmin for years. Back in the days before Debian/Ubuntu hit mainstream popularity. I'm no stranger to odd error messages, but none of my google searches found any illuminating fixes for my problem. It finally fixed itself, but it was annoying to have my phone reboot itself at random times.
6) Stupid capactive buttons. Hopefully HTC has fixed this, but I'm forever swiping one of the buttons with the side of my thumb and zipping back to the home screen
7) Lack of OS support. I'm running Froyo on my phone because the officially supported updates stopped after that. I should probably consider myself lucky that I even got Froyo to begin with! I'm not interested in custom roms, so I never tried to find out if I could run newer OSes on it or not.
8) The messaging app sucks. I can't search for contacts by name, it pulls up some of my facebook contacts - which aren't even in my contact list - but not the one I wanted to text.
9) AT&T won't let me sideload apps without a third party sideloader hack, which means getting the nicer free apps from the amazon store is more work than I'm willing to do.
Other than that it's been a good phone. It normally just works, the speed is OK, I like the HTC Sense UI. I like the photo widgets that let me have pictures of my cats on my home screens, and the agenda widget. I like the scrolling background. I like the call quality and the speaker quality. Points 1-9 are dealbreakers though.
I would hesitate before trying Android again. I won't say I'll never try it again though, because every time I say never I end up doing exactly that. (/me looks at her netbook running Ubuntu - I swore I'd never use a non-windows OS on my computers...)