PM specops420 on JOC, he will tell you all about his love/hate relationship with SAWs.
They are fun when they work but a heavy POS when they don't.
IMO stick with an M4/AK until you've gotten some more experience. Learn the basics then branch out from there. You've gone through 3+ guns in 8 months? Yikes. I've been playing for 5 years and am only now considering trying a DMR set up.
No need to rush things.