Given your specifications, I would recommend that you swing a 31" 28oz bat. The main difference between this 2018 Rawlings VELO BBCOR Baseball Bat: BB8V3 and the Combat Maxum will be the material used in construction. The Velo utilizes a one-piece alloy construction to provide a stiffer and louder result on contact. The Maxum is a one-piece composite bat that will need a slight break-in period but should reduce vibrations felt on contact. Any recommendation will be determined by preference in material.
The 2018 Rawlings VELO compares very similarly to the 2018 Easton Beast X Speed in that they are both very well balanced, one-piece alloy bats designed to emphasize bat speed. I don't think either one have a significant advantage other the other in terms of pop or sweet spot size. As for the 2017 Rawlings Velo vs the 2018 Rawlings VELO, they are very similar in construction, yes, and are still made of the same alloy. If you can find the 2017 model in the size you want, I would probably recommend that over the 2018 just to save some extra money.
The 2018 Rawlings VELO BBCOR Baseball Bat: BB8V3, 2018 Louisville Slugger Solo 618 BBCOR Baseball Bat: WTLBBS618B3, and the 2018 Easton Beast X Speed BBCOR Baseball Bat: BB18BXS are all very similar bats. All of these bats feature one-piece, all alloy construction with balanced swing weights. If you've had success with one of these brands in the past, I recommend staying with that brand.