After the novelty of highly situational TRAC-5 S underbarrel launcher wears off, go Lynx or Jaguar for an actual good gun.
Stat wise, the Trac-5 S seems identical to the default Trac-5. That said, I looove the grenade launcher. Especially if you are higher up than your enemy. Defending bases I love spamming it from above. Yes it will reload, I just put the ammo box down, launch a grenade, and do anything to interrupt the auto-reload (I hit T) and it will restock/reload just fine. That said, I seem to lose 90% of the time when it comes to in base 1v1 at close range, it just takes a shiat load of bullets to kill people sometimes.
TRAC-5 is way better than the S variant in my experience, the higher RoF just makes it better for me. I've got the nade launcher on the S variant but I don't particularly like it as it is currently tedious to reload, perhaps when they fix the resupply bug. I've got the lynx as well and I have it fully kitted out, and I honestly hate it, technically on paper its better than the TRAC-5 but in practice its way more inaccurate. Have not tried the Jaguar yet but I've heard good things about it. All I want is the ability to put soft point ammo on my default TRAC-5, then I'd have the perfect gun.