Title pretty much says it all... Guild is just trying to progress in TOGC for the first time, and we aren't really sure which fight we should try and stack up healing on. I was thinking Beasts and Valks, but I'd be interested to see what other people do that run it successfully.
It really depends on your healers capability and classes. If you have two good healers one a spec that excels at tank heal (Holy Pally, Disc Priest, Shaman,) and a good raid healer (Resto Druid or Holy Priest) then they should be able to two heal all of it. If you don't have the perfect raid makeup I would recommend 3 healing Anub, Valks and maybe beasts, but Jarraxus and Champs are relatively easy to deal with. This is me assuming since you are just starting TotGC that you aren't very geared but If you are, almost any decent healer with ICC 10/25 gear can 2 heal all of the bosses.
We are running a shaman and druid healer. We are clearing the first 4 bosses in ICC 10, so some icc and 25 man gear. On beasts I'm worried about a healer getting a snobold at a clutch moment if you only have two.
With a shaman and druid you should be fine on beasts if your shaman gets the snobold your druid should be able to keep everyone alive along with your shamans instant cast heals ( Earth Shield, Riptide , Nature's Swiftness ) as long as the DPS turns and burns it, and if your druid gets the snobold its even less of a concern since we can easily keep raid alive with our instant casts alone.
At least run the Northrend Beasts with 3 healers. I recently two-healed it (Druid + Holy Priest) and it is far more relaxing with 3. Twin Valkyrs were the next difficulty in terms of two-healling, though not as bad as the beasts, but you may want to do it with 3.
Jaraxxus and Anub are easier with 2 in general. On Jaraxxus you have to kill the portals/volcanos quickly and anub can be zerged fairly fast in p3 with one dps more. (Also, if your dps isn't that good, you may have problems with getting into p3 within 1 burrow phase)