Long post follows. Apologies.
Aggressive mechs that are powerful? Raider/Raider G2 is my vote for you (more health than Berserker, not dependent on an ability timer for high damage 1st strike). Berserker 2nd vote. Vanguard 3rd vote (fastest C-class).
Cheap response = get them all, you won't know til you try everything, and your opinion in the end will likely not be the same as the 'general consensus'.
Honest response = for me (only), those I've played with feel that the most looked down upon choices are Tech, Incin, Rocketeer, and Brawler. Tech is easy to score with (heal everyone all the time and arrive at the top of the scoreboard), Incin has limitless ammo if you can get the timing down, and anything with Hellfires as a secondary are sometimes seen as needing less skill (lock on, fire, hide). Doesn't stop us from playing them, though. People in other crowds and brackets will sometimes disagree with this assessment. See previous posts 
But...indivdual skill and comfort with the platform/weaponry count for much more than the mech itself. There is always an exception to the rule. I've seen aggressive Sharpshooters/Reapers go toe-to-toe with foes, I know a Tech that goes aggressive 1vs1 and repeatedly comes out on top, I've seen Infiltrators that only use their cloak to escape AFTER they kill you. But these are exceptions, playing against their typical roles (Snipers/Reapers hang back, Techs only play a support role, Infiltrators sulk around like ninjas, etc.).
It's a very rare player that hasn't bought a mech or two that they just couldn't wrap their head around, or was never able to achieve mastery with. If you play long enough, you'll eventually have them all - and you'll buy them with HC anyway, just out of curiousity.
So try something different each time (an Assault is too similar to the CRT you already have). You will get burned once or twice, then later you will find one that's "OMFG this is so awesome" good.
And there are some really skilled, scary players that pilot the 'looked down upon' mechs too.
The most important thing is get out there, practice, and have fun. And occasionally try following others around and just watch what they do - easier to make observations while you're not the one being shot at. ESPECIALLY watch when you're angry that someone is consistantly mowing you down like grass - actually the WORST time to quit a match, and the BEST time to learn. This is a 'never stop learning' type of game. Figure out how to counter instead of repeating mistakes in the hope that the result will be different 'this time'.
Good luck.
Edited by FlamingBeaker, 25 March 2015 - 05:20 PM.