Either is great
Hayden,
Either of those would be a good choice, with one caveat. The caveat is the M4516, make sure you get one with a dash number (-1 or -2) in the Model number.
fed168 is right, the very early units, marked as "Model 4516, without any engineering changes had some problems. The problem, as I recall was with slide mass, and comparing the non-dash units to the later -1 or -2 pieces, you will see that the slide on the later units is a bit "beefier", which lends credence to the earliest units having slide inertia issues (?)
So, just stay with the later units, and you should be fine. Also, the 4516 is an all-steel piece, which gives you a little more weight, and possibly a little more "longevity", but that is for time to decide. I actually prefer all steel autos due to that factor. A good holster and belt is the great (weight) equalizer IMO.
The M457, and all the Value Series autos are just plain great values, again IMO. The M457 was the first compact .45 Smith auto to use an alloy frame, and I believe it to still be one of the great "sleepers" in the line. The internals are the same to the M4516, but cost has been saved in appearance details, due to a few of the "extra" milling steps left out, leaving you with a fairly square slide. (Some S&W guys don't like the lines, but if you like Glocks....... need I say more? 9X19??)
So, if you are looking for "similar" dimensions, keep this in mind. A M4516 will fit into a holster made for a M457, but the opposite will not be true, due to the dimensions and shape of the M457 slide. I am of course talking about form-fitted holsters.
For the record, I own a M457, a M4513 (Performance Center Shorty 45), and have owned two seperate M4516's (both -1's), and have not had any problems with any of them.
.......SmithNut
......SmithNut