Well of course, my number one main is Meta Knight. I have two secondaries (secondary and thirdary? they're about even I'd say...) I'm not an expert with my secondaries, Im only an expert with my main ^_^ but I'll try to give advice on their strategies as best I can, but if you need more information, I suggest visiting their own character threads.
Marth
I mained him for his playstyle and his coolness (the tiara almost kills his coolness but whatever). He was also my secondary in Melee. Good approaches with Marth is the same as Melee, jump fair fair (wall of pain). Marth can also chaingrab certain characters very well (falco). His side B is much faster than Melee and the final slash when pointed up has a lot of knockback. His nuetral B MURDERS shields. When charged properly, it can also be used as a good recovery (if you're high enough away from the stage). His up B is also good as a kill move if the situation demands, but I find his fsmash my most common way of killing. Marth's dair is a meteor smash which is always nice to have (I wish Meta Knight had one but that might be a a little overpowered). Marth has no lag when landing after his fair and a lot of lag for his dair, so keep this in mind will fighting (short hop, fair fair, land, fsmash, niiice...).
ROB
I mained ROB for his unique playstyle and because I just love that robot ^_^ His spot dodge is very useful to attack or grab out of. His nair is just a great move altogether, large range covering all sides and it's pretty strong. Uair and bair are also quick and powerful. Down B is useful to limit the movements of your opponent and nuetral B is good for a quick attack to rack up some percentage from far away or to knock your opponent even farther away from the stage when they're already off. Nuetral B and down B can also be used to get your opponent away from the ledge when you're trying to get back and for spacing. I don't really side B at all...Up B is great because it's a recovery move that goes very far, but once you start it, the only thing you'll be able to do is a normal air attack; you can't airdodge or do anything else until you get hit or land on the ground (or grab the edge). ROB is a great character for gimping, like Meta Knight; follow your opponent off the edge, knock them farther, and get back. And like Marth's dair, ROB's dair is a meteor smash (or spike, I dunno).
Hope this helps ^_^
