I have the 763e with the Vanderbilt tender (incorrect - the NYC never had any Vanderbilt tenders - which is funny, considering the founder); mine now has a correct PT tender. The locomotive (only) is basically a re-issue of the pre-war 700e. The sound is pretty good, but has only 1 chuff per revolution, which is irritating. There is a way to fix that (to-do list). Mine runs well and smoothly (and quietly for a Pullmor loco). I like it. The detailing is just what you'd expect - exquisite for the 1930's, still good today. A good model. Tough. Built like a household appliance; geared well (fairly low). All it needs is a proper tender.
I also have the early version of the L-3 Mohawk; mine has been converted to a can motor with ERR Cruise Commander and Railsounds. The "Sound of Steam" was awful. It did run fairly well for a Pullmor, also, before it was converted. The detailing is really pretty good, considering that most of it is cast-in. Lionel did drop the ball on the valve gear, though - incomplete and it shows. That could probably be improved with some work and some Hudson parts. (To-do list.) I have never been around the later version of this loco.
Prices of both seem to run $500 or so...? Check eBay listings and Completed Listings to get a real-world feeling for it. Some of the 763e's have been real bargains - if you can live with that tender. Not sure about the Mohawk.
I would not pay a lot for either - not that they are bad, but they seem to go for moderate amounts, and their running characteristics, in stock form, are definitely out-of-date - but that's not a fatal flaw.