W'rkncacnter
Hero
So I'm going to throw out a controversial opinion: I think the ideal starter class is rogue, not fighter. Everybody knows about ninjas, and the single die of sneak attack, no maneuvers, and a single skill trick is a very simple build. It'll still be lots of fun to play, though, with extra damage a lot of the time, and the power fantasy of being the sneaky person.
i mean, remember that OP is asking for 3rd level characters, not 1st level (whatever you might think of that). both of these classes have maneuvers by level 3.you're not wrong. Berserker could also be argued as a nice starter class. Large HD makes them tough, no maneuvers out of the box, rage is fairly simple to manage, and there's a lot of well known inspiration for the class as well.
so, if we're going rogue, i'd probably suggest the burglar, because the only thing you really get from that at 3rd level is some better expertise and either the ability to reroll 2s on attacks and ability checks or better sneak attack dice. if we're going berserker (i would absolutely not give a new player a berserker if we were starting at level 3 solely because of furious critical), i'd probably suggest the rager, since it's essentially just being harder to kill and being more accurate on the first attack each turn.