The easiest/most versatile build is probably the ammo-chain with juggler build.
Fin/Jug/Fin/WizK/SoaB/SoaB/TH/MAch/(then either iron man until the end or another triggerhappy to up the plasma/chain-gun damage).
It get's you off the mark quickly, with juggler offering massive versatility. Carrying two combat shotties, you can also switch out instantly to a single/double for up to four shotgun blasts without a reload. The more "normal" quick-slotable weapons you carry, the more versatile it is. Just carry 2 exotic/uniques (or shotties for scouting) and quickslot to whatever you need at the moment. A walking arsenal of death. Change from shotguns to something else as they lose their edge.
Whizkid comes online at about the exact same time you do the chained arena (letting you do something nice with the agility mods there). A nice, accurate chaingun/plasma early on is very helpful. Plus you can start packing bulk/power mods onto armour/bfgs/shotties so you don't have to have them wasting backpack space. Tech/agility mods are for your plasma rifle.
Then you slowly up your damage with your weapons, get better with your chaingun/plasma and then finally need no ammo for them. None. You can happily fire off a plasma all day without caring about cells, letting you carry a nicely bulk-modded bfg9k that's always fully loaded.
A really easy build. Early, easy shotgun/chaingun usage that moves into better chaingun/plasma usage as the game gets harder. Plasma ammo isn't a problem (so you can wing off rifle shots for small guys/bfgs for big) which helps a lot. Then it just makes you tougher to kill (with maybe one more shot from your plasma rifle if you want it).
The standard "easy" build. Quick start-up, mod-able weapons/armour, good end-game. Works well even in hard mode (where one shotty blast isn't enough, but two does fine). It's the best, for every non-challenge game(IMHO).
