>>11467496NECA figures have decent enough sculpts (mostly), paint that ranges from quite nice to pretty sloppy, mostly sub-par engineering, but often have really, REALLY bad QC. Figures breaking out the box is not uncommon, and stuck joints that will snap if not carefully unstick with hot water (assuming you realize it's stuck before you try and move it) are extremely frequent.
Sadly this board has an absolutely pathetic shitposter who relentlessly shills/runs damage control for NECA and will accuse anyone who criticizes NECA in any way at all of being a "troll". He's made any discussion of NECA impossible because the moment anyone reports QC issues he accuses them of lying/trolling.
In answer to your OP question, there really isn't a definitive accurate Alien. The Revoltech is a little too stylized and quite small, the Mafex is super fragile, NECA is as mentioned a crapshoot, and the SHMA is a fiddly mess with some weird inaccuracies. I'd say if you need a poseable Big Chap that's primarily based on the actual suit (as opposed to Takeya's artwork) the Revoltech is still the best one all these years later. It's got issues but it's got the fewest problems of the options available.