One thing you have got to be really careful about. The SII does not have a flap over the micro USB port (Not like the Samsung wave). Therefore moisture and dust can get into the port and cause havoc. You will find the MTP and Car navigation functions going on while the phone is off and basically sucking the juice off the battery in less than half a day! In this case all you need is a tooth brush and some iso propyl alcohol to clean the port. The electronics contact cleaner can do too. (This is one thing i had to learn the hard way) I do not know if the SIII has a similar prob. I would expect an improvement though. By the way the batt on the SIII i a whopping 2100mAh. That is huge. But then again you have got a quad core processor...

Having used HTC desire and now galaxy s2..
This is the phone to go for..galaxy s2 is among the best unless
you want flagship s3

How is HTC desire compared with s2 galaxy?

I don't own either but from comparing the two on GSM Arena, I'd go for the LG purely on hardware though it has a slower processor at 800MHz compared to the Samsung's 832MHz. What it lacks in processing power, it makes up for in RAM.

HTC desire run on 1.0 ghz and galaxy s2 on 1.2 ghz
both smartphone.the reason i changed my phone to s2 was HTC had problem with voice transmission to other end and low phone storage but s2 is opposite.
ticks all the boxes for me.