I don't have the 745 but I do have both of the Al-Mars you are considering. I also have 15 or so other models from Benchmade and carry a mini-RSK as my EDC, so I do have some confidence in BM.
All of these are pretty close in design, lock style, and size. The 745 will have a slightly larger blade than the Al-Mars and it will be S30V instead of VG-10. I guess it depends on what you plan to do with the knife. S30V is a nice steel for slicers, and it can take some amount of hard use, but it's not as flexible as VG-10. The VG-10 Al-Mars should be a bit tougher in terms of impact resistance, but if that's not a concern for you, then BM's S30V is really sweet to sharpen and use. And I've had no chipping issues with any of my S30V from BM or Spyderco.
My opinion? I love my Al-Mars. They came as sharp OOB as any Spyderco I've ever owned, the lockup is rock solid even after some months of use, and I really love VG-10 as a great all-around steel for a folder, especially if it's a slightly larger knife that might see some hard use. The G-10 scales that Al-Mar puts on the liners was a perfect fit all around the edges and it's nice and grippy w/o being damaging to fabric or skin. The rest of the F&F on my Al-Mars was also first-class, and the Nomad has a flat ground blade that slices as well as any knife I've ever used.
I don't have a 745 because I don't the looks of the knife. I didn't like the Lum designed Spyderco, either. Of the two Al-Mars you've listed, I would probably get the Nomad first because of the usefulness of the flat ground blade. If you want a real low-rider, however, the mini-SERE is the best choice. The clip attaches to the butt end of the knife so the whole knife except the clip rides out of sight.
Whichever you get... enjoy!
