KingRyan

Yea most get some use with their unique types. Rotom-Fan suffers from so many being better electric types and better flying types but it's still usable. Heat and Mow are pretty solid as well as their types are pretty good. All in all, the others do have use, you jsut got to find it since they aren't as across the board good as Wash.

Wash pretty much has the advantage of "I've got one stupidly predictable weakness". Grass isn't exactly the most common type of attack and most Mons outside of Grass Type have pretty limited access. So, it's a lot harder to leverage that weakness then say, the water weakness of Heat, or the Fire weakness of Mow since Water and FIre are much more common and spread types of damage ((also SR isn't fun for Heat, Frost, or Fan. THat's another thing to remember.))

Short end, in most cases Wash will always be the one you use in OU other than suuuuuper fringe scenarios. It has the hands down best sig move in Hydro Pump and the least weaknesses with one to a very uncommon attacking type. Te others shortcomings don't make them unusable, and they do shine in their own right for sure though.