OK of those units you mention only a deltec offers the ability to directly feed the skimmer from the overflow. The ASM requires mods to do that and you can't do it with the Tunze.
The Tunze is a interesting unit. I have the smallest of the new DOC units on my office 55g and it definitely produces skimmate and it's really quiet. It does NOT overwhelm you with bubble/foam production etc....but it definitely works. It's very hard to "compare" it to the others, but if you like Tunze, you'll like this skimmer. But do NOT expect to plug this thing in and see oodles of foam.
ASM will be your bargain unit. Again, it "works". Just drop it in and turn it on.
If you can stretch for a Deltec then I'd go that route. The AP600 is PLENTY for a 54g tank.
Finally, yeah you can get into all sorts of I got this blem and this mod etc... and if you're a DIYer (I am not) then go for it.
Finally if this is your "final" tank, ie there ain't no way short of moving that you're gonna upgrade for several years, then stretch the budget every which way. If this is just a step on the road though....maybe start out with something more modest to gain experience and then when you setup the "dream" system...