I'm still having trouble picking out a secondary for Wario. For me, I struggle a lot against sword users, namely Marth and Link, as well as the more zoning heavy characters, like Villager. I'm also absolute garbage against Yoshi and Falco. I'm okay against characters like Rosa and Mario who are considered high tier, but I haven't fought a good Sheik yet. I only know she's a hard matchup.
I'd ultimately prefer not to play a fast rush down character. Though I understand Fox is a viable option, the play style doesn't really mesh with my mindset while playing.
So far, it's been a toss-up between Ryu, Diddy, and MGAW. Ryu has good spacing and powerful tools, and I'm familiar with his inputs. Diddy covers matchups like Yoshi and Villager decently, but I'm struggling a lot with banana and kill setups and learning what to do in the neutral. MGAW is more of a wild card. I feel like he functions a lot like Wario and because of his light weight he doesn't get juggled quite as hard. Plus, I think he can do fairly well against Sheik, though I'm sure the work you'd have to put in is astronomical.
Other characters I've used before are Mario and Pit, who are solid, easy to use characters, but I'm still iffy on how they would handle Wario's bad MUs. I also enjoy Robin.
I just want to clarify that I should be putting more time into Wario for learning those harder matchups, but I'm not opposed to putting the time in to learning more characters. I've clocked nearly 400 matches in with Wario, which may not be a lot, but I have no intention of stopping with him. I simply feel that having a secondary will keep things fresh, especially if they're fun to use and I can work them up to an acceptable level.
Any feedback would be greatly appreciated! Even if it's tips to help cover those tough matchups.
EDIT: I've gotten some advice from the skype group, and apparently the best choices I have are MetaKnight and Villager. Ryu is also a good choice because of his ability to play footsies and punish.