That said, unless for other reasons not stated, you have a desire to get into an old, rag-wing taildragger, I'd suggest going with the 172 for your instrument training. First, practical instrument flying in this century pretty much means using a GPS, and that 796 doesn't count as a GPS for IFR operations. Second, you may find the cockpit environment (noise, temperature, etc) in the 172 much more amenable to learning.
That said - I agree with Ron that you should go with the 172N. Most of the approaches are RNAV approaches now and it's good to know how to fly them and how to setup the GNSS for the approaches. The GTN 650 is nice when it comes to unpublished holds as it can be programmed to fly an unpublished hold. Use the AP or hand fly and follow the magenta line. (After learning how to setup and fly holds the old fashioned way first.)
Interesting. I did most of my training for instrument in a 172S G1000 w/ integrated GFC700 autopilot. I was told by a DPE those hours do not count for commercial unless they were logged in accordance with 14 CFR 61.129 with that specifically noted in the log book. OTOH, I have also heard from other CFIs that was not the case. In any case, I would like to get a clarification as I am planning to do commercial next on the way to CFI and I need to plan what all training I need.
As long as those log entries use the words "attitude instrument flying," "partial panel skills," "recovery from unusual flight attitudes," or "intercepting and tracking navigational systems", the time counts for the 61.129(a)(3)(i) requirement. There is no requirement that there be a specific reference to 14 CFR 61.129(a)(3)(i) in the log entry. Any DPE who says otherwise should be referred to his/her POI at the FSDO for the correct guidance from AFS-810. And that C-172S with G1000 and GFC700 meets the TAA requirement in 61.129(a)(3)(ii), so you can do all your Commercial ASEL training and practical test in that airplane.
I don't often fly IFR, but when I do it is in a Mooney.