What you get with a quality aftermarket trigger is a consistent, smooth and PREDICTABLE clean breaks with a typically lighter pull and many times shorter reset.
One of the best budget all around 2-stage triggers as mentioned before is the G2S. Nice clean break that is predictable and not too light. They are robust as well, and would feel comfortable about it lasting a long time. For a nice single stage, again and mentioned before, the CMC (I prefer their flat bow model as well). Probably the best single stage feeling trigger I have used. The flat bow is very comfortable and is super clean with a nice crisp break. They feel darn near as good as a 2-stage.
RRA makes a super cheap 2-stage, but I am not a fan of the feel of them. The pulls aren't always very smooth from the factory. I'm sure you will see them recommended though.
I do think it's worth the cash and Geissele makes a nice all around trigger.
Curious, what do you want to spend? Good triggers run in the low $100 range on sale, up to $375 for some 2-stage or fully adjustable units.