I am currently an Apple Person. I used to be a HTC person (windows, mind), but I always found that the sound quality in calls poor and that the build quality was also quite poor.
I have had three iphones now (I am very good at getting early upgrades!) and I really like them, but I am a total technophile and I am one of those - oooh look at that new thing, I must have it NOW! people.
The reasons I ike the iPhone is not the interface (as I figure all mobile phones are pretty damn easy to work out how to use), but just that they do everything I want them to and I find the build quality very good and the call quality very good and it has a great screen, but without being to big and bulky. The Samsung Galaxy Note looks amazing, but that's going to take up too much room in my handbag on a night out. Added to that, when I picked one up, it kept slipping out of my hands as it was just too big for me to grip).
I was EXTREMELY tempted by the Samsung Galaxy SII, as my dad got one. But I found it very cheap feeling and as though it would fall apart at the first available opportunity. However, it does have a better screen and a better camera than the 4s. Also I am put off by the NFC chip in the phone. In this day and age, I want the banks to make it harder for other people to use my bank account should my bag get stolen, not easier! (I think I might also like them to make it harder for ME to empty my bank acount too! Maybe a little sticker on my card saying "Are you sure you need this?!")
I wouldn't buy a HTC Android phone, as having spoken to people who work in phone shops, these have the second highest return rates amongst smart phones (following Sony Ericsson - JEEZ SE, have you STILL not worked out how to make a phone that works, yet?)
Having said all this though, my favourite phone of all time is my Nokia N95 8GB - that phone rocks and is pretty much indestructable. Had mine since 2007 and it's still going strong.