So, into which category do you fall?
As a very general rule to which many exceptions exist, if OTR fits you fairly well, you will tend to get "more for your money" when buying OTR, than when buying MTM, assuming both suits are comparably priced (and that the price is below about $1000.) And no, I can offer no proof of this - it's just a conclusion I've reached over time. My guess is that it's due to various cost savings having to do with inventory issues and economies of scale which are available to an OTR retailer like, say, Brooks Brothers. Savings which are simply not present in anything like similar degree to the typical MTM tailor/retailer.
That having been said, if for whatever reason it does make sense to go the MTM route, I'd surely prefer having the tailor measure me in person, to emailing my various measurements to someone.
As for the MTM suit being full canvas and the OTR suit being (presumably) half canvas (as is the case with Brooks' 1818 line, I believe)... look, I get that one of the first things someone who starts educating himself about quality suits learns is that full canvas is quality, and half canvas is garbage. But the truth of the matter is, a current (yes, there have been significant improvement in this area over the years) half canvassed suit can actually be okay. And a full canvassed suit can still be disappointing.
I'm not denying that if I were dropping thousands of dollars on a bespoke suit, that I'd want it fully canvassed. Certainly I would. But I am suggesting that it's sometimes easy to place too much emphasis on this one point, to the extent that it takes on undue importance in the decision-making process - particularly when you're talking about quite good half canvassed suits, and relatively inexpensive fully canvassed ones. (And sub-$1000 MTM pretty much qualifies as relatively inexpensive.)
Oh, and particularly if you rarely wear suits (which you state to be the case), and therefore probably rarely need to have them cleaned and pressed, I wonder if the full vs. half issue might not be even less compelling. (At least in my experience, frequent cleaning and pressing will tend to exaggerate the difference between full and half canvas.)
Well, just some things maybe worth considering.