Steve, Having been to both resorts We prefer SB, saying that, this year we are going to GS staying at the Iberostar Obzor Hotel.
SB is a very flat resort,no steep roads etc., to worry about, whereas GS is built onto a hill and if you happen to get a hotel in the back of the resort then be prepared to come back fitter than when you went.
Both resorts have plenty of nightlife and decent restaurants, both food and drink prices are very,very cheap compared to say Spain. Ample choice too, Chinese,Indian,Local cuisine etc., In GS there is even Big Ben's fish'n' chips shop.
Plenty of self catering in SB ( look at map to see where the apts are though ) if in a hotel try and get B&B. Sometimes if we like the hotel we have gone H/B but still always have our evening meal out.
Hope this is of some help.

Toonman