Well, I'll rank the mainline Solid games as they were the ones I've played.
1. Metal Gear Solid 3
2. Metal Gear Solid
3. Metal Gear Solid 4
4. Metal Gear Solid 2
While 3 is definitely my favorite and 2 is definitely the "less good" game ('cause it's not bad, won't call it worse XP), 1 and 4 put quite a fight between each other, with 4 even having stuff from 1, and actually a piece of that game, both were also great games for their time but I think 1 has such a great amount of thought put in everything that it deserves to be over 4.
Just to get a somewhat better idea it would be kinda like this:
3 >> 1 > 4 >>> 2