I've stayed at Wesley for a semester and loved its so ill just outline your options from my experience.
Since you want to enjoy yourself college is the only way to go as SUV at least has basically no social life, terraces and Darlington are probably somewhat similar though i dont know.
Since your a guy your options are Wesley, St andrews, St Pauls and St Johns (sancta and womens are obviously out cus ur a guy).
Im sure Pauls my have some hot guys but since it only has guys and being a guy yourself... unless your from rich sydney private school and know lots of people going there it wouldnt be my first choice.
Wesley, Drews and Johns are all coed, going to Wesley id say its the best but Andrews and Wesley are fairly similar culturally so there isnt really that much difference. Any of the colleges will have plenty of social stuff going on so should be right at whatever you just have to get into one.
You have to apply and go for an interview, factors they take into consideration on who is let in are whether family has gone there, sporting ability, academic ability, cultural stuff like music etc. If you dont have any of these just try to impress in the interview
. Id just apply around. Since college basically everything like food it probably doesnt cost all that much more than SUV and is just way better.
Also i wouldnt worry about the religious affiliation of the colleges it doesnt really make any difference.