Snake's "bad" matchups are: Olimar, King Dedede, ZSS, MK, ROB?, Falco, Snake, Marth, with Olimar being the worst.
Falcon is really bad in brawl <.< Marth would be a good pick because he counters Olimar and Falco, and does well against Snake.
Other suggestions are: MK (duh), Falco, Peach
Actually, the correct method is different for vertical survival verses horizontal survival:
Vertical: Bair and Fast Fall
Horizontal: Uair, Fast Fall, then second jump.
Thread:
http://www.smashboards.com/showthread.php?t=244091
The Boost grab timing is at the very beginning of the dash attack, dash attack and then immediately grab. You can also grab by doing dash attack -> shield. While your at it, learn Boost Pivot Grab too.