I have to say that my favorite are the MKIII Armour. They just look tough. The bolters look a bit odd laying there, but they have some shots of some models holding them and they look great. These would work really well for converting some Sternguard.
The price on these kits isn't too bad for what you are getting. These are complete models - you don't need a set of plastic marines to put them together. The price for the Marine kits is about $35 US Shipped. You are getting half as many as you would out of a plastic box and that is fair for the quality. The bolters are about half that, so about $16 shipped - those end up being a bit expensive, but would be worth it for converting up Sternguard models.
All in all this is a really solid release and I hope they put out more sets of the older armour - even some sets of the newer armour would be welcome.