I saw this post and forgot to answer it I'm so sorry
For scientist, you want to balance out HP and AC. You won't have a shield so you're either a glass cannon or a bulky murderer depending on what you aim for. The best pet is Tenter Lion V1.
Light dragons (priests or wizards) go with MA as SheepieChan stated above. Dark dragons primarily focus on MA, LK, and HP. The best pet for both dragons are either Karan 300, Odinea 300, or Tutankhamen V1.
Buffalo depends on what you want to do. Gladiator, I suggest either AP and HP (since you won't have guard like Mercenary does). For Mercenary, you're going to want to go pure AP since you'll be protected by Guard for the most part. Depending on what route you want to go, whether it's bossing, PvE, or PvP, that's up to you in terms of attribute. Air-type skills are the best for bossing and PvP (don't take my advice on PvP, I don't do that) whereas electric-type skills are best for PvE. If you're just going to grind, focus primarily on Lightning Strike and Earthquake Blade since they'll be your main skills (plus their cooldowns are roughly consistent with each other so you can use them back to back). The best pet is Count Blood 300 for both Gladiator and Mercenary.
Hope this helps!