For me, since I really like Wario (He was my first "Mario" character ever), I almost always use him for every opportunity I get for playing as him (With the exception of Super Smash Bros., for which I mostly use Pikachu there)
He's not my favourite to play as in every game but for the most i play him rather often.
If it's something like Smash Bros. or Mario Kart where it matters i would play him in a casual match but i'd rather stick with my characters that i'm better at.
On the other hand if it's Mario Party and it doesn't matter i'll go Wario all the way (and Luigi too).
Every single time Wario is a character, I use him 80% of the time. That's true for 95% of the games I played that include Wario. Smash Bros is the exception, because he's just a "for fun" character, and I mix in with Samus.
Quite a lot of the time. Have to admit, I'll sometimes use a different character if they're a higher tier or what not, but Wario is usually my main man now.
He's always one of my top choices along with Toad and Luigi, even in 64 DS where his use is admitingly limited, I still like to use him for the added challenge that his lower jump provides.
Smash For is the only game where I won't even touch him anymore and it's not just bitterness over the charge being gone and his new side smash being shite, but also the fact that For has Meguh Mayuhn and I'm sorry. There's just no competing against him.
I use Wario every chance I get. I love the character so much! If I'm playing with friends and someone picks Wario before I do, my brain just sort of shorts out and leaks out of my ears. I can't comprehend not playing as Wario.
I have considered dropping him in Smash 4 though, considering that in my experience he's absolutely awful, especially compared to the DLC characters. While I've probably spent the most amount of time playing as him, I tend to get better results with Wii Fit Trainer and Olimar.
The game I use him most in is Smash, despite my overall dissatisfaction with his portrayal there...he's still a really fun character to play as and I'm not afraid to admit that I get amusement out of farting on my opponents.
In kart racers I'm not a huge fan of heavyweights, so that unfortunately means I don't play as Wario much in Mario Kart. And that's the only multiplayer spinoff series I frequently play, so most of my Wario playtime is in his own games and in Smash.
Although I did play as Wario a lot in Mario 64 DS, but that was a long time ago. Haven't touched that game in a good while now.
Everytime if possible. I also get really into character and act like a complete jerk to Mario in games such as Mario Kart, and I steal stars from him in Mario Party.
If the difference in stats actually means something in a spinoff game, I'll take that into consideration; otherwise the default is Wario.
For example, my main in Mario Kart is usually Toad because Wario tends to be too slow for me, but in MK8 I use Wario since there isn't enough of a difference between characters (as far as I can tell) for me to care about my acceleration points or whatever.
In every other game I'm usually him (except for SSB, I can't get the hang of him). I mean, who the hell doesn't want to see Wario ice skating in M&S Olympic Winter Games??? It's hilarious.
This is gonna be blasphemy, but while he is definitely my go to Heavyweight, I don't use Wario very often in the Mario spin-offs or Smash as I'm not usually into heavyweight characters most of the time.