Dane,
Congrats on your decision. I think you'll be really happy with the MB.
As you know I have had both the TWB and the F21. Here are my thoughts...
Make the decision based on looks, not function. They are not different enough to make a difference. With that said, here are the subtle differences I have noticed:
1) The F21 bow is not that much bigger, if at all. This surprised me. It is just as wide at the windshield and obviously wider at the nose , but not quite as long as the TWB (windshield to nose). So if you are sitting facing forward with your legs up, your knees will be a bit more bent. Make sense? I think the pics you posted show this. Personally, I don't care because nobody over the age of 12 is ever up there in our boat.
2) The F21 interior width is actually less than the TWB. Yes, both boats have 100" beam and are plenty wide. But the F21 has wider gunnels by an inch or so on each side. So the resulting F21 interior width is 2-3 inches narrower than the TWB. I knew this when I got the F21 and didn't think I'd notice. But I do. It's not a huge deal; doesn't affect how many people I bring along. It just seems a little smaller inside to my eye. Could also be that I went with a much darker interior on my F21.
As I said above... these are very minor differences. So go with the boat that really makes you feel excited. Frankly, given the way you like clean and simple designs, I'm surprised this is even a question.
One last nit pick... the F21 pics you show above are actually a 2011. Here are the same pics of a 2012.