No one really answered your questions....
Regarding Tamiya Sherman kits, any would do, as the M4, M4A3, and M4A3 105 all saw action there. So you can't go wrong with any of them. From Dragon, you could use the M4A3 76w Battle of the Bulge kit, the new M4A3E8 that's JUST now coming out, the Expo Albin Ircyk one, the M4A1 early, the M4A1 Operation Cobra one. Also, the Italeri M4 Marines (which is actually an M4A3 just like the Tamiya) or the M4A1 w/76 gun, their old kit, which is still quite nice. They also do a sort of cobbled together combo now of an M4A3 76w, but I'd go with the Dragon "Battle of Bulge" one instead.
These are the main ones you're likely to find in photos of the time period as well as on your hobby shop shelves.
Oh, the rounded hull types are anything with A1 at the end, ie M4A1. The A1 denoted the rounded, cast hull. So, from above, an early one with 75mm gun would be the Dragon M4a1 early, and then for later, 76mm gun versions, the "Cobra" one above or the Italeri one. Tamiya doesn't make any with that hull.
Then there is the composite hull, available as a Firefly kit 9037 (Dragon), but the new one doesn't have an extra turret, only the firefly turret, so you'd have to get a turret from someplace else. The composite hull, as outlined by someone else, featured the cast front identical to the M4a1 76, but then had the squared off back of the regular m4.
hope to help.
Rob