We don't seem to have a lot of information at this point as to what the bulkhead seats are like after the reconfig. (I'm planning to have a look in early July when I fly in 22C and will report back if no else has beforehand). While they are labelled as MCE, I'd be worried that the bulkhead seats would actually not have that much extra legroom.
I've done the exit rows on the 777 many times. I don't worry about having a window but YMMV. As for if it gets cold, it didn't bother me overly. However, it really depends on how you dress for the flight. Shorts & sandals might not be the best idea. It has been a while since I've been on an AA 777 flight so I don't know if they still give out blankets in the main cabin. If not, consider taking your own.
Personally, legroom is my main selection criteria. For my upcoming flights I had selected the exit rows. But having heard the report above from Andi28, I decided to give 22C a try. It should have the same legroom as the exit row, but it has the advantage of being close to the front of the main cabin and theoretically allowing me to disembark somewhat quicker. The major disadvantage of course is that there is a window and middle seat passenger potentially needing to get by you during the flight.