I'd go Braviary all the way. Here's why
1. You don't have a Flying Type, which I think is really useful for in-game, since it's a good typing and you don't have to swap out a Pokemon at the nearest center in order to use Fly, which is really convienient. Plus you can find it on an interation on Mondays at Route 4, starting at the decent level of 25, unless your super far in-game, your not gonna find a better way and it has a really good stats, better defences and SP Attack than Excadrill. Plus, in finding an Excadrill, you have to find a Dusty Spot that just happens to be right, which could take forever. Excadrill does have better typing, but Braviary is just way better and more convieniantly suited for your team, for example, all of it's weaknesses are covered by your other members, whereas with Excadrill that's not the case.)
[email protected], possibly Sharp Beak or other attack boosting Items.
I read the suggestions and followed them, and Fly is pretty strong, STAB, and is a super useful HM to have on one of your party members instead of having to try and find an HM slave like I said above, plus it's Flying STAB that doesn't have recoil.
As for Moves for your other Team Members:
Samurott's fourth Move: I'd either recommend having a stronger Water Move, such as Hydro Pump at 62, or Hydro Cannon, the Water Starter Move, or, if you wanna have a more Diverse typed Movepool, Dragon Tail as a TM.
Haxorus's Fourth Move:
You already have good stab, so I'd suggest an Ice Coverage Move, in case Arcanine is out, or at low HP, while still being strong, such as Brick Break.