Let's see, HTC Desire, released in February 2010. Single core 1st-Gen 1GHz Snapdragon processor. Prohibitively small amount of internal memory for apps. Stuck on Android 2.2 Froyo (developer-only 2.3 release available but not recommended). No likelihood of being upgraded to 4.0.
Samsung Galaxy S II, released in February 2011. Dual core 1.2 or 1.5 GHz processor. 2GB storage for apps. Currently on 2.3, to be upgraded to 4.0 during 2012.
Don't get me wrong, I love my HTC Desire. Rooted and running CM7, it is still so good that I still haven't seen a phone I want more than this one (I love the 3.7" form factor, and I don't play games).
However, the SGSII is a beast compared to the Desire, and still one of the very top phones out there. No competition.