if you are building a basic and first time build, I would just go with a standard lpk.
the brownelles bushmaster one I think is the cheapest right now at under 50 bucks.
If you have a FFL friend that can order it for you, you can get it at 40 I think.
quality name brand, so no issues.
Palmetto state armory has sales in the 40-50 dollar range for theirs and they too are fine.
people tend to stay away from the PTAC line however, so pay attention. some say they are ok, others did not like them.
price diff is usually only about 10 bucks, so not worth the risk imo.
the "higher end" not necessarily better, but could be considered better by some, would be the RRA or CMMG kits you see out.
they generally run around 60-70 bucks. sometimes you can find them on sale at places.
Generally there are 2 or 3 guys selling these on the equipment exchange here.
Any of those should be fine, from any of those sources for a basic build.
people that talk about better triggers etc are talking about how the trigger feels when shooting.
and while that can be important, it is mostly for accuracy improvement, not just having a basic build.
when you get to that point, you might have a few gi trigger and hammer sets laying around after you replace them.
otherwise, what you get in the kits are just fine.
wait till you have shot it a bit and decide. don't just upgrade now. it could be 40 to 300 bucks you never care to spend if you are happy with what is in the kit.