I haven't played MGSV (aside from their expensive little demo they released first which was kind of cool but didn't blow me away) so keep that in mind.

MGS3 is definitely the most impressive game out of the others on a lot of levels, and probably the best technically, but MGS1 is still the best in the series for me. It's got enough interesting little tricks and easter eggs in it to be interesting without suffering the bloat the series started to feel later. It also just plays beautifully and doesn't weigh itself down with so many game mechanics that can make parts of the later games an annoying mess sometimes. MGS3 was just teetering on the edge of that when it came out but I feel like after that it was just downhill into a mess of cumbersome controls and gameplay mechanics that occasionally get in the way more than they add to anything. MGS1 is simpler, it's streamlined, and it's an utter joy to just sit down and play it. Honestly, I think the simpler mechanics serve it well by letting you just slip into the proverbial zone and enjoy things. In fact, I'd probably even rate VR Missions higher than things like MGS4 because of that.