I have only used a few, but have been really impressed by the X10. Good friend of mine has the Galaxy S and it's camera is garbage compared to the X10....but it was much faster when I was on 1.6. When I moved to 2.1 it got a little quicker.
Now that I am using a special image that has all the Sony junk off the phone, it works just as fast as the Galaxy....in fact, I got him to download a benchmark app and ran it and I beat him.
I had my phone a couple months before him (Galaxy wasn't available till 2 months after the X10) and I didn't have to pay 100 bucks plus be locked into a 3 year contract.
I am happy with my x10...I find people who hate it or have big complaints about it haven't set the phone up the best way they could...
If you simply use the Sony setup and then give up and hate the phone then congrats on your future paper weight. I am happy, phone working smooth and loads apps just as quick as the rest, but I feel bad for the people using the generic setup....or the people still stuck at 1.6.
Some people already have 2.2 installed on the x10...the community is our future, not Sony.