Recently changed phone and compared the HTC Desire, Nokia N8 and Samsung Galaxy S. Decided that Blackberry wasn't for me as most had a small screen and was unsure about signing up for Blackberry e-mail. I needed more information about it. Symbian appeared slower but a good camera on the N8. Android 2.1 and then upgraded to 2.2 swung it for me. Good OS plus allows tethering which I understand Windows Phone 7 doesn't. Samsung had the better screen but no flash. I have a good camera so went for the Samsung. Samsung predictive text is very good.
I suggest that you go in and have a look at the screens. Some are bigger and brighter than others. I find that the built in diary and contact manager is fine and sync the diary through Google calendar. I think that Samsung have good screens but their PC sync software Kies is imo fairly poor.
This may seem a bit of a basic question, but some areas of modern technology are a bit of a closed book to me!
Further to my comment above about some handsets not being available on my network, if I purchase a sim free phone of my choice, is it just a matter of transferring the sim from my current phone to the new one?
I appreciate that I may have to tell my network what I have done.