First off, I have to say that there aren't any of your sculpts I've seen that I look at and think, "yuck!", so that is a good thing! Of the ones you've posted I've built two of the three Thor IIs, the gravedigger, both centurion Omnis, and the resculpt centurion. Of those, I like the centurion Omni the best, with the Thor II a close second. So far, I think the top half of the gravedigger is some of the best work I've seen you do. The bits for the cables and ammo feed were a nice addition that were easy to adjust for fit, and I think the proportion, detail, and resemblance to the art is spot on. The legs LOOK good, but they are ramrod-straight and very close together. Nothing I did with them looked very natural because they were locked out straight, and with the hips so narrow relative to the rest of the mech, I really wanted to put it into a walking or running pose.
I'll echo that I think mechs look better in motion, like walking or running. It's like pictures in car magazines: even a Camry looks better if you get a picture of it leaning through a corner instead of sitting still. I think the striding pose also helps hide any awkwardly sized hips that the original art may require as well. Setting up your legs for a more dynamic stance to start with, especially on the ones with humanoid legs, or at least putting more bend in the knees, would be a welcome change.
Other than that, I think you learned your lesson about details on the Thor II. It definitely feels like the torso is a little plain in some areas, but I still like the mini better than the original. I thought the detailing on the centurions was much better. For whatever reason, I feel like I was able to get some of the most pleasing poses out of the centurion Omni, of the mechs you've made. I thought the variants were well executed, although I really wanted the one with the hatchet and shield! I liked your attachment for the jump jets, although if that rail was just a mil or two wider it would have made magnetizing the jets easier...but that is probably a pretty niche complaint.
When it comes to your post-and-hole joints, I'm of two minds. They are certainly strong, and for the bigger, more boxy arms like the pendragon and Thor II B and torso to hip joints, I think they are great. However, there are times with the hips and shoulders where ball joints would allow for a wider range of angles for mounting. Especially where a mini has very narrow hips, I feel like ball joints help get a wider stance instead of forcing a more parade-rest look. For shoulders it's kind of a toss up. I kinda wanted them on the Thor II prime and the cent omni's fist arm, but didn't miss them in the centurion resculpt
I must give you extra kudos one one thing: you did a great job in the little cylinders on the cent Omni. I hated those things on the ghost, but they were super-easy to work with in the cent. I was very skeptical, but they were no trouble at all to install.
Lastly, I would like to suggest a couple minis to take a look at for ideas for leg and joint execution: the shoulders on the reseen Battlemaster are some of my favorite ball joints. You can't hardly make them look bad, and you have huge freedom in posing them if you want. For legs, I think the recent shadow hawk resculpt did a nice job of including a dynamic pose with a simple construction that didn't take many parts. Also, I think the Vulpes had very poseable, but very forgiving legs. I remember both of those as being pretty easy to put together into a decent looking pose. There are others as well, but I can't recall them at the moment.
In general, just keep up the good work. No one is perfect, but overall I like your style.