LCT make some of the sturdiest guns on the market, I don't know if it's the best, some people are E&L fanboys, but I've never tried one so I won't comment.
I believe all three of those have the same gearbox, and the externals will be solid too, so it's all really preference and how much you'd like to spend.
I haven't seen many RPKs, and I don't think I've ever seen an RPD, so it'll be a head turner
My friend has around 5 LCT guns and I have one, neither of us have had any issues with it, compared to king arms, g&g etc, it's massively better (IMO)
I've fallen over many times with mine, I've knocked it hard against walls, trees and there's still not even wobble in it. Compare it to my g&g ak, which snapped in half when it fell over from leaning against a wall... xD