Most people make Strider because they see them deal lolable crits in youtube videos and in the actual game. Okay, sure, they deal loads of damage. . . But at what cost? It takes skill and a great Internet connection to be a "successful" Strider, and honestly, if you have the necessary Internet connection, you'd be better off as a Saint or Elemental Master. Though it obviously all comes down to certain preferences.
Underrated: Elemental Masters (ESPECIALLY ones of the Fire/Earth variety)
Elemental Masters have to wade through a lot of bull crap since magic isn't the fastest thing around, and having every other class easily out damage you for more than half the game (level wise) is extremely discouraging. But as any Elemental Master would tell you (and show you), it all pays off in the end. Biiiig time. Oooooooh BIIIIIIIIG time. Now GL getting to level 110, nubs!
If we're talking about PvP, it'd be Gunderpaherps for overrated and Meisters for underrated. I would say EMs for being underrated, but magic is actually quite hacksy if you have the connection for it. Or gear for it. Or evasion stacked for it. Or PvP skills for it. Etc. Most people count Meisters out because they lack range and move slowly, but any decent person using a Meister = deadly. Just ask all the people I fought with mine HAHAJAYKAY! You can also spam turrets and run like a sissy, but that's not fighting, sillyheads.
"He who fights and runs away, lives to fight another day!"