I have bought from MB. For 14 x 12 one has to use two supers as a 14 x 12 brood. I screwed them together. Not ideal and who knows whether they will extend their range to that version of the National format. I would hope they will, as I suspect it will do the job with ease.
Not enough detail to give a good recommendation, but you need to consider compatibility with your other kit if you intend to retain some or all.
There are issues with all the suppliers. MB is one of kit needing to be modified and that 'lip' may prove a downside; Paines of unproven, as yet, durability/robustness; BHS of no data; Lison of incompetence; Sweinty of cost and possible quality control.
Your poll is slightly flawed in that you may get biased replies from those who have not really considered the alternatives. In other words, the blind leading the blind!!
Paines appears to be less robust than the MB construction, BHS and the Paines will not accept National roofs, an issue should you wish to use that 'total compatibility claim' by them but overwinter on a totally poly unit from brood box up, in that you need to retain both roofs to use timber shallows as supers.
Bee space is also an issue, but not one that cannot be overcome. It does need consideration, all the same. Unframed slotted steel and plastic Q/Es are not much good on TBS, IMO.
Even though my MB nucs required modding (for the extra deep National frames) they are proving very robust - I can jump up and down on the units as the roofs are more than adequate to take my 800N force.
There are, of course A-belo (Lysson manufacture) where they are now trying to sell off hideously out-of-spec hives (presumably the moulds are being corrected but they may not be easily sorted and who knows whether their 'sold out' claim is really the truth - I very much doubt it is!!)
Sweinty - ahh yes, even heard reports of chewed hives, so they don't seem to be bullet-proof either. Depends on whether they are competitively priced, if that is a consideration.
Does that help? It does show that I have considered the whole range. It might even be better to change to Langstroth format. I'm not, but ... there are a lot of them out there ... possibly more choice and certainly more experience of them.
RAB