It depends on what you're going for. If it's just the win/full-win, then I tend to think that HMP/UV is the best thing to learn from. I rarely play on anything else.
For a few nice early builds, here's a couple. In no particular order.
Scout. Int, Int. Go for shotguns early, but build into weapon-type after.
Rel-Rel-SM. Can still go for plenty of different masters after this. Easy arena run on UV.
EE-SoB-SoB-TH. Masterless build. Highly effective.
SoG-SoG. Pistols ahoy!
Technicians. Throw a tech-mod on a shotty. Easy early game.
Build into MFa. Very (very) strong build. Rockets and dodges and shotguns. Yay.
Fin-Jug-Fin-WK. Switcheroony with big, modded weapons and armour. Freaks with technician's quick medipacks. Still great with any class though. EE or Rel afterwards.
There's a hell of a lot of builds that work. DPS, ease-of-use, speed, damage prevention/soaking, anything. To tell you the truth, there's a few OP builds in DoomRL, but virtually any build you take has it's niche. Just focus on 1-3 weapons or character attributes and build around them. You can't have it all. Assemblies are a part of character building, but so is non-assembly modding. Just make sure you shine in a couple of areas and be happy. Or go for MAD or Vampyre and laugh.
Note: scouts with Int(2) are great when you are learning the game. It's a crutch, but you will learn a lot from using it.