I guess I'll do my opinion on Wario.
Neutral B
Chomp: Bread and butter part of Wario's arsenal. It's a command grab that can be held to catch sidesteps, has very little start-up and ending lag, and can negate projectiles. Lacks any real flaws outside of its short range.
Inhaling Chomp: Adds a very powerful suction effect that draws people from a good distance. Wario can't bite his victims as quickly as with the standard version, but they usually break out after one or two hits anyways. The most noticeable downside is that you can't end the bite until the suction comes out, which makes it slightly more punishable then the normal bite, but it's not too terrible.
Garlic Breath: Extremely slow, plus the stun from it doesn't scale with damage and your opponent can mash it out of it before you can even follow-up if the move connects early. Not at all worth it.
Side B
Wario Bike: It's a recovery move, a powerful KO move if you can drop a wheelie on people, a throwing weapon, and a pseudo projectile if you jump off of it while it has momentum. Has 18 HP, meaning only charged projectiles and smash attacks will be destroying it.
Speeding Bike: Has higher speed and fixed knockback then the normal bike, but no real KO power and only 5 HP, along with the inconsequential downside of being unable to turnaround. It's much better for recovering, punishing whiffed attacks, getting people off the stage for attempts at gimps, and can even lead into combos at certain percents. For Warios who like gimping, this is the custom of choice.
Heavy Bike: Gains the ability to bury opponents and has a massive 40 HP, making it a viable shield from projectile weaponry (Diddy's accursed bananas especially), and a better throwing weapon. Moves slowly, which is a double edged sword, as while you can't use it as a punish, it can catch spot-dodgers and doesn't take any effort to keep it on the stage for use as a throwing weapon like the other bikes. Has no real KO power and is much worse as a recovery move due to it dropping like a rock and Wario leaping a lower height from it, but is still functional in that regard. Good if you like throwing the bike around.
Up B
Corkscrew: A very basic move. The damage and knockback aren't good enough to make it worth using as an offensive option very often, but it does its job as an added recovery move when the bike isn't good enough.
Widescrew: Sacrifices height and a little damage in exchange for much greater control over its trajectory. Better offensively then Corkscrew due to its completely horizontal launch trajectory and being able to reach opponents from angles Corkscrew can't.
Corkscrew Jump: Grants a bit of extra height in exchange for increased starting lag, no hitbox, and no control over your trajectory. The extra height isn't worth the added risk of being hit while trying to recover due to the lack of a protective hitbox and predictable trajectory.
Down B
Wario Waft: Takes ages to charge (One minute and 55 seconds, minus one second per item eaten), but once half charged, has an extremely deadly combo of speed and power. Fully charged is significantly stronger, but also noticeably slower and more predictable, so avoid using it unless you're far behind on stocks or percent and need to make a comeback. If you're confident with your aim and like getting early KOs, this is the preferred version.
Rose-scented Waft: Loses the massive KO power that makes the standard version attractive in exchange for a much faster charge time of one minute and the relatively useless perk of planting flowers when it connects. It's meant to build damage, but Wario is already a pro at doing that.
Quick Waft: Takes a mere 30 seconds to charge fully and gains two seconds of charge per item eaten. KO power is significantly lower then the normal Waft, but higher then the Rose-scented Waft and still much stronger then any of Wario's aerials, which makes it excellent for gimping or as a finisher when fully charged. Preferable if you aren't very precise with your wafts and/or like gimping.
Overall, I'd say Wario has a pretty good set of customs. None of them seem overly situational and have easily utilized perks to them.