out of your selection – i’d be sticking to a steel 29er so the right size Swift, but there are plenty of options available
i’ve suffered with back problems in the past and tried lots of different HT frames, (in a very rough order of uncomfortableness on my back) such as, Dialled Morning Glory, Orange Evo2, Cove Hummer, two 29er Scandals, Brodie Holeshot, Cotic Roadrat with drops, Evil Sovereign, a rigid Salsa Mamasita, Cotic Soul, GF Ferrous 29er, custom Lynskey 29er, On One Ti29er, – the most comfortable ones being the last (all 29ers)
a 29er wheel (cause of the length of the spokes) also provides a bit more comfort/give over a 26er wheel