The Marth matchup is a very pesky one indeed. In my experience, this matchup is really bad on Yoshi's and FD, but maybe that's just me. Some of my biggest advice may be to play like a floaty. Playing like a floaty is generally important for the neutral game in most matchups (except maybe Falco, Falcon, and Fox, depending on you and the opponent). Playing like a floaty also changes your combo game a bit. Stringing together fairs into a final nair once you run out of stage can be effective, but if spacing/DI makes it risky to hit the nair, don't.
Another key point that I have found is not using your double jump cancel a lot. You can bait using empty DJC -> wavedash if it's used seldomly. In too many cases, though, Marth can just hit you out of your DJC if you mis-space it, leaving your already vulnerable recovery to be your only option.
Obviously, Dream Land 64 would be your ideal stage choice, since it's Marth's worst stage. I feel like Battlefield is a perfectly reasonable pick, and Fountain of Dreams isn't too bad.
Oh, and two more things. You can watch Vrud vs Tai at EVO 2014 for an idea of how Vrud handles the matchup. And if you need any clarification, you can PM me if you don't want to ask on here.