I personally really like Slip Bomb and Sliding Fortress.
Slip Bomb's "bombing" part is still appreciably strong, and not too weak compared to the default, unlike the wind bomb. For the air version, it seems that Bowser gets to the bombing, descending part noticeably faster than the default, as well. For the ground version, I like to use it to force trumps/edgeguards. Slip Bomb's shortened travel distance means that, for the most part, Bowser can walk up to the edge (even to his "teeter/totter" animation), do Slip Bomb, and still grab the edge. Though it seems to be actually stage, dependent, it works more for me on FD than Arena Ferox (both standard and omega), for example. If timed right, it's like I can force my recovering opponent into a lose-lose scenario: Either they get bomb'd as they recover, or they grab the edge, only for me to trump them just a mere split second later. In the event of the latter, Bowser can follow-up on the trump with a BAir or some other mixup. In either case, he still gets the potential for hefty damage.
Again, just my personal opinion.
Sliding Fortress is a decent escape option, and actually has a rather hard-to-challenge hitbox, it seems to be larger than the default. Compared to the default, it can go almost as high with decent mashing. Unlike the default, it can be made semi/somewhat safe on block, due to the speed and horizontal travel distance. It rewards with less damage, but is actually a nice way to get opponents in the air, in which Bowser can punish well.