Huhu,
i would suggest the vanguard too, it should fit your playstayle, because the vanguard is a fast mech for even c-class and the grenade launcher is very good to play againts A-Class peek a boo players, due to your high amount of HP, you have the upper hand in most situations, but you need a very good mind for positioning yourself in a good way.
The submachine gun is already pretty powerful, if you have a very good aiming, for mid/short Range!
Maybe the infiltrator will suit your gamestyle also, its a pretty fast mech with the same weapons as the vanguard, with the ability to be invisible for a short duration of time (it uses fuel). So this mech is good for fast ssasination (alphastrike - Grenade, Detonator + SMC after that, don't use SMC at first, you have to surprise your foes at first).
In that way you are extremly effective againts players like me, who are playing technician, dueto the low amount of HP. If someone hits me after your alphastrike, iam dead for sure. If you do it right, you can be very fearsome for techs, so they wont be agressive healing at the front anymore and stuck in the background provides only support for teammates coming back from the frontline.
And please dont listen to this Eliteshooter Guy.
Good luck and have fun 
 
Kind Regards,
Galaxy Radio