Lrm mechs can be great to play but play them to their strengths. Do not sit at almost max. range and just chuck missiles at locks your teammates get for you. Most of the time you'll waste your missile due to intervening terrain and losing your lock, these things are only worsened by the time it takes for the missiles to actually get to the target.
Stay with the group and give direct support, try and make sure you yourself are seeing your target for maximum efficiency. Less chance of your target hiding behind terrain, less chance of losing your locks and less travel time = good damage.
With that out of the way I've enjoyed 2 missile mechs a lot, I'll illustrate both with Smurfy links:
Centurion AL:
http://mwo.smurfy-ne...d542231a7a4bb44
Great medium missile support mech with 45 salvoes of ammo and a very respectful 4 ML back-up arsenal. It requires an expensive XL though and a DHS upgrade. I've left of the Endo upgrade but it's a worthwhile upgrade that gives you even more options. You could take even more ammo, or you could instal Artemis launchers. Or maybe you'd like to drop a bit of ammo and change those ML to MPL's. Or drop some ammo and go for Lrm15 launchers (this last one would leave you with too little ammo IMO). And the extra half ton could be spend on a bit more AMS ammo.
And there's the Awesome 8R you mentioned:
http://mwo.smurfy-ne...da2c615d33a10f2
It has got an even more expensive XL engine to keep up with the pack and the mandatory DHS upgrade as well as Endo and an Artemis upgrade. You could forego Artemis and use the freed tonnage and slots for even more ammo. There's also the option of dropping that head mounted ML and getting a TAG there. Personally I like the extra ML, often near the end of the battle when I've run out of ammo I've presented the battered enemy with a fully armoured assault mech wading into their lines. My best yet is getting 3 kills with those lasers alone.
Regardless, it's a monster missile mech with those 4 Lrm15's, and it can hammer enemy mechs into the ground.
I've just acquired the Hunchback 4J that was mentioned above and it also seems a good missile mech. Same goes for the BattleMaster 1S. Due to its tube count that one's better for 2 Lrm15's and 2 Lrm10's though (leaves more weight for ammo).
Lastly my personal opinion on Launcher sizes. Medium should use Lrm10's, Assaults should use Lrm15's, and no mech should use Lrm20's (just too big and heavy for what you're getting). Lrm 5's are interesting as they can be a great troll weapon on any mech capable of mounting enough of them (5 or 6), and can be a nice way of getting in some extra assists for some more close range oriented mechs.
Good luck and don't let the haters complaining about no-skill Lrm noobs get you down. It's easy to chuck some Lrm's, but it takes skill to make them really count.