TL;DR - I enjoyed Forbidden Door slightly more than MITB because while both events were of similar quality overall, Forbidden Door gave me more of the results I wanted when it came to what I was invested in. However, I like that the WWE is keeping its B-level events to 5-6 matches.
Elaboration: Personally, the result of a match I'm invested in and how that result is delivered makes a difference on how much I enjoy a show. Especially if I am more invested in a given show.
If I have Forbidden Door and MITB on a similar level as far as match/event quality, the tiebreaker will be "As a fan, did I get the results I wanted?" and unfortunately that weighs heavily on MITB because I had more investment in the event as a whole.
I did not want Drew to win MITB, mainly because his big feud at the time didn't need the briefcase to be involved or wasted on it.
I did not want Sami to win.
I did not want Damien to have another title defense mired in controversy.
I'd say the only result from MITB that I was 100% happy with was Solo pinning Cody, and even then I wish the Bloodline had dominated the match more. The women's MITB match was the only one where I didn't really care who won and perhaps unsurprisingly, it was the match of the night (and probably better than every other match that happened except Swerve/Ospreay). Despite these results, every match was good or better.
With Forbidden Door, the matches I cared about ended with the result I wanted to see, except Mone/Vaquer, but that's because I went into it wanting Mone to win only to start rooting for Vaquer midway through it.