Originally Posted by theworld
I would say go Thameslink (or whatever its called). Its a pretty fast train, only stopping off a few times (I think Clapham and East Croydon). By the time you get to Vicotria and walk from the tube to the train, etc, timing will probably be the same.
Thameslink doesn't stop in Clapham - I think it's pretty much London Bridge > East Croydon > Gatwick and then onwards.
I tend to use Thameslink/FCC if coming from Canary Wharf - much easier than schlepping over to Victoria.