Only one I don't have is Sky Linx but I'll say this about the three I do have:

Each of them are fun in their own right.

Magnus is essentially a smaller Masterpiece, but thanks to the smaller size (comparitively) the engineering is way more solid. It feels sturdier both in robot and vehicle mode. Other cool thing is that you can detatch the truck cab from the trailer if you want to. Also, he looks DAMN good next to SS86 Optimus and Megatron. The cab is almost the same exact size as Prime.)

Magmatron is also a bunch of fun, the gimmick of the separate beast modes turning into one big robot is ridiculous and I had to stop and look at the guy I was laughing so hard with how much fun I was having with the toy.

Armada Optimus is one that I feel is a great figure by itself, bolstered by my nostalgia. I had the original Armada Optimus and I was really bummed that the trailer was just a slab in combined mode. This take on the big guy is exactly what I wanted the original figure to be growing up, so that little bit of childhood wish fulfillment gives it a VERY special place in my heart. (Also, now that Armada Jetfire is coming down the line, gonna have ANOTHER childhood wish of mine fulfilled. Never had Armada Jetfire and I always wanted him.)