talal janab nice question
well it depends on the preferences what you actually want from your device nothing else
if you go for the ranking then every reviewer has its own preferences actually in gsmarena ranking samsung galaxy s was on the top for many months and now its on 5th and htc desire on 8th
websites k chaker me paroge tu bus hogya kaam
Advantages of SGS over Desire
1) Super Amoled Screen 4 inches over Amoleds and Slcd
2) Built in storage 8gb/16gb with micro sd over just micro sd
3) bluetooth 3.0 over bluetooth 2.1 ( i actually dont use bluetooth ) 
4) Better camera with 720p recording but without flash over mediocre camera search youtube with galaxy s and desire samples
5) Secondary camera for video calls over No secondary camera
6) divx /mkv support over mp4 etcz
7) 1500 mah battery over 1400mah
Advantages of Desire Over SGS
1) HTC sense UI over touchwiz ( truly i dont like any of these i love stock one in nexus s and nexus 1 )
2) HTC built quality over plastic build of galaxy s
My preference will be SGS over desire because
I love to keep my media files in my cellphone cuz i go to my village every week so i need music videos and super amoled will be enough and music quality matters more to me
i need battery backup cuz i talk alot on the phone and text alot and listen to the music alot
i am a previous owner of iphone and touchwiz is identical to the ios thing so touchwiz will be my preference
i need secondary camera to make video calls on skype and fring
So What are your preferences ?
jo acha lage le lena =d