Bastiodon is an amazing wall with incredible defenses. He has a big movepool and is a very defensive Pokemon. He has good enough HP and the ability to learn many awesome walling moves. Some are Toxic, Curse, or Attract. He's quite powerful and can also work as a Stealth Rock setter if you need one.
Rampardos (or Cranidos) is a powerfully offensive Pokemon with the second best Attack in the game. He can OHKO just about anything with a Choice BAnd/Scarfed Head Smash STAB, but has bad Defenses and Speed. He needs a Focus Sash to survive properly but if he gets a hit in can pretty much always OHKO. Sheer Force will help even more with boosted power for moves like STone Edge or Thunderpunch.
Overall I say Bastiodon is better with great defenses while RAmpardos is a suicde sweeper.