First 3 concept look like suit upgrade LV1~3 . The 2nd suit and 4th suit look good for me but the shoes look like they can't have speed in the water or they would have backpack that help them move quickly in the water? I like the helm on 3th because it is more possibility 1st one nice too but 360 degree glass design look not so safe for them. Anyway, all of them are great design, I would like to see your project in the future.
I see alot of great concept ideas here. Personally, I would choose as a final design a cross between them. (Assume what I talk about next is using all the pieces from left to right in the order of 1, 2, and so on.)
Specifically, body 4's suit structure but with the coloring of body 3's material. From there, I would use Face 1's facial hair as a base and darken/ make it thicker and maybe go so far as to also add face 3's mustache and hair. That's just what I would do though.
The only criticism I have is the flipper feet. To me in design and practicality, they shouldn't exist as part of the suit since it has a much more wetsuit/ skin layer feel to it; they should be something in addition to it, not part of it.