Bay Lake Towers has access to Contemporary and all its amenities. Walking distance to the MK. Great views of the MK and Bay Lake. On the monorail so you have access to Poly & GF easily. Ferry rides to WL & FW and THEIR amenities. Nice new pool area. Major con: Bus service to the rest of the parks can be, according to what I've heard, a bit lacking. Some people don't dig the decor. If you're staying in the Studio, they're amongst the smallest.
Saratoga, you're walking distance to Downtown Disney, plenty of restaurants/dining options, Disneyquest and great for the shopaholics. 2 nice big pool areas, one of them really new, plus a smattering of quiet pools. Quieter. By being so close to Downtown Disney, you're also close to bus service that'll take you to any other Disney resort; if you like to visit or dine at other resorts and you don't have your own car, that can be invaluable (of course, BLT has the same option being so close to the MK, but once you're that close to MK who wants to take a bus to another resort
). Also closer to at least some "nightlife" venues if you've a mind for less theme park-ish entertainment (Cirque, performers at Bongos or Raglan Road or House of Blues, the movie theater). Great spa on premises. Treehouse Villas if you've a mind to be really remote. Turf Club is a pretty nice restaurant that rarely gets too busy to take walk-ins. Close to golf courses if you play. Cons: It's really big and spread out. The food court (Artists' Palette) often gets packed. Same deal with buses (at least you're rarely sharing with other resorts, but that's because Saratoga's so big there are like 5 bus stops within its route). The theme of the resort is more muted compared to most other resorts (but then again, so is Contemporary, which some people describe as resembling an assisted living community highrise); however, it's still very pleasant, and some people don't like getting hit in the head with Disney 24/7
I think what you choose will depend a lot on what you want out of a trip. If you're traveling with really little ones, I'd suspect walking distance to the MK would trump everything, but older kids/teenagers might prefer being close to the giant mall that is Downtown Disney. If you're park commandos you may prefer BLT; if you prefer a more relaxed pace of a trip, or someone wants a spa treatment, being in SSR would seem more suitable.
Final caveat, both being DVC resorts, it will probably be easier to book at SSR over BLT, especially since October's "only" 9 months away, so a lot of BLT members will have booked trips already (whereas SSR, for all it has to offer, tends to book later, with more members who call it a "home" resort looking to switch at the 7 month window). If you're not a DVC member, paying cash for your room, I'd suggest trying to book sooner rather than later so you have a better chance of getting either of them.
