I'd have to say LA c4 has been the best bang for my buck purchase by far. 3k+ kills for minimal certs and effort. Other than that, dual grinders and extended mags is a purchase I look back on favorably. While I don't play Max much, having the dual grinders seemed to have a huge impact on my effectiveness and I would definitely purchase again.
QCX Hunter, totally useless. maybe I'll add the explosive to it, see if it helps, but I can't see killing anyone with it,, by the time you get another shot off, you'd be long dead.
max-rank Magburner - definitely my best purchase! even after one and a half years close second would be max-rank repair tool and medic tool
In order: Pre-nerf shotgun Pre-nerf tank mines Sirius Pre-nerf ZOE Pre-overhaul rotary Med-tool Pre-nerf dual cosmos Dual blueshifts LA C4 Pre tankmine nerf mineguard on sunderer Post tankmine nerf Blockade sunderer.
Best for the certs/SC: Thermal on Prowler HEAT Autorep/Thermal on Lightning Second Pounder arm Jaguar Ext. Mag on the free shotgun TSAR-42 PDW (I don't think it's that great but got it for 1 SC and considering TR's other options...) Biggest regrets: Striker Hailstorm Lynx Cougar (I didn't expect much but had to try it :/) CARV S Skyguard
max rank on lockdown for my TR max. The carnage you can unleash with a pair of pounders and a decent position is beautiful. Absolutely beautiful.
I don't know...there are so many things Alpha squad pack mayber. I've heavily used each of those weapons and saved the 6month boost after the buff to it.