Hey, I don't have any BM knives with the coating so I can't help you on that aspect, but I would recommend the satin finish. Like a lot of people have already mentioned, it is really nice looking and easy to maintain.
In my experience, Benchmade's 154CM is just fine in terms of rust resistance. I have the 940, 520, 580, and 746 Mini-Onslaught and none of them have ever developed rust, even though I have fairly sweaty hands that seem to rust metals pretty easily. I've carried the 520 Presidio everywhere I've been, and through hot and cold, dry and humid, it doesn't seem to be effected at all by rust. The 746 being satin finished will probably keep rust away too. The only stainless steel I've ever had problems with were 14C28N Sandvik, and that was only because that steel was bead blasted. Also, I have slightly oily hands that leave fingerprints like crazy, and I've never had any of the fingerprints leave rust, but I do take very good care of my blades.
In terms of blade coating, I would recommend the satin finish. In my personal experience, every time I pulled out a black coated knife, such as my M16-01KZ, every single one of my friends who know I'm a knife guy were like, "Woah dude, are you going to stab someone with that?" and I understand why. The black blade seems to associate the knife with being more stealthy and tactical to some people. The satin blade has a very nice look to it, and in my experience, it seems like people are bothered by it less as long as you aren't showy. Finally, the knife itself is, in my opinion, pretty classy looking even though it has a modified clip point blade. The nice shape of the blade combined with the curved handle has led to many of even my non knife friends to ask me what kind of knife it was. It seems to have a classy look to it even for a clip point knife, so people don't seem as bothered by it in comparison.
Hope this help you out man, I seriously love my Mini-Onslaught, no matter the version you get, I think your going to seriously enjoy it. It really has good bang for buck. Congrats
Edit: I also have a review of it in the knife review section, its pretty lengthy, but it fills in a lot of info. Hope this helps you out man. I'll probably update it soon with a bit more use.
Also, the knife is a great EDC, its thin so it slices pretty well, and it seems tough enough for most everyday stuff. Not saying it is weak, but it isn't a prybar. As a student, its cut everything I've needed to cut, including some plastic, paper, and other miscellaneous small stuff just fine.