Species resistances/weaknesses are now gone with the new BD, no more 40% air resist from Pteris or Grundos taking more damage. All species are the same, only the picture differs.
Agree with @
(you need an account to see links) with Lennies(ys?) being the most versatile BD species in regard to weapons. Having 2 species 100% freezers and a 50% species healer makes them the most affordable species when you start to get into high-level battling.
If a Lenny is not your thing, the next most popular species would be the Kacheek, Gelert, and Elephante, just for their cheap 50%+ species healers. Other species have specific 50%+ healers too, but they're r99 and too expensive to justify a pet morph.
(I used 'species' a lot in this post, now that I read it,
)