Which is better for my team, Lucario or Ferrothorn?

Ferrothorn is FAR better than lucario. Lucario dies to anything that can outspeed him or can take a blow. Here's the analysis:

Lucario:

Can do a physical or special sweep set, both with a priority one move.

Relatively fast.

Doesn't cover much. (Has fighting moves, crunch, stone edge, dragon/dark pulse. Nothing else worth mentioning)

Get's KOed easily without his focus sash.

Ferrothorn:

Can stall, set up, annoy, or simply wall.

REALLLY SLOW (but you can take advantage of that with gyro ball)

Resistant to almost everything other than fire and fighting. Can still take a blow or 2 from fighting moves.

Forced to switch out instantly against fire types.

Conclusion: Ferrothorn is better than lucario by a little. My recommendation is in Ferrothorn. He is strategically more diverse. you can turn him into almost anything, even a heavy hitter with a curse/gyro ball set, or set up with stealth rocks, or stall with toxic. Ferrothorn's role can easily change by switching 1 skill while lucario is locked into being an end-game sweeper.

Get an Excadrill! Jkin

I would pick a Ferrothorn in your team, because it lacks a wall. Ferrothorn's a good entry hazard deployer, and able to put down leechseed. Guranteed to destroy your enemy if they haven't got rapid spin. Roar, coupled with entry hazards (and dragon tail) is pretty good on Hydreigon. Because Hydreigon is a mixed attacker.

You have enough attackers so thats why you need a wall.

However, Ferrothorn is almost get killed in 1 or 2 hits by a fire type move. Gyro ball will be pumped up to the max with Ferrothorn's ultra slow speed. (Ferro's speed is on par with Jigglypuff. That says alot)

Ferrothorn is good at absorbing both physical and special attack skills, so its good for absorbing hits by stronger pokemon (that may 1 hit ko your sweepers). and is resistant to 10 types! Immune to poison (same as Lucario) but is supereffective vs fire and fighting.

Leechseed, stealth rock, gyro ball, (explosion? maybe good for an exit vs a top sweeper)

Goodluck!

Ferrothorn def. Give it a rocky helmet.

I'd recommend lucario, because it can learn a larger variety of moves.