I would do whichever option is likely to be quicker, knowing that the 4:00 to 7:00 window on party days tends to have low crowds, as those in the park earlier in the day know the party crowd is coming, so they are leaving...while many of the party crowd doesn't show up until 7:00, leaving a nice low crowd option for two or three hours. When we have been for the parties, we are not in a park earlier in the day, so we tend to try to make an ADR at a monorail resort around 2:30 or 3:00 and then hit the MK hard at 4:00.
With that said, if you will have been in the MK that same day already or within the same trip, then this brief interlude may not be as important from a timing/riding standpoint. In that case, BOG is much more relaxing, with a pretty cool atmosphere. Having done BOG and not feeling like the food quite lives up to the hype, I'd probably still stick with Plaza, but if you've not done dinner at BOG yet, it's definitely something you need to do, just for the atmosphere.