Question

Rock tomb or flamethrower for garchomp?

Comments

What format?

Answer 1

There's no perfect answer for this. I would say it depends on the rest of your moveset, team, and where you're playing too. I realise that's a bit of a stretch, but it differs from case to case. I'l give you the pros and cons to each, so you have a better idea:

Flamethrower:

• Good, because it catches some opponents off guard. Ferrothorn hates it, for one. More experienced or risk taking players go for Fire Blast to ensure a KO.
• Bad because it has better Attack than Special Attack. Maybe Fire Blast with the extra power makes it more usable, because what's the point of it if you can't KO the opponent, right?
• Good, because coverage against Ice and Steel is good. Although, sticking to STAB Earthquake is fine in most cases due to its sheer power and frail opponent defenses, in case of Ice, and the 2x Weakness in case of Steel.

Rock Tomb:

• Good because you can hit the flying types that EQ can't touch
• Great because it slows the opponent, which is always (>99%) good.
• Bad because generally Garchomp is faster (not always. This is why it's easier to decide if I know where you intend to battle), so you don't need the speed drop
• Bad, because Stone Edge and Rock Slide are generally more favoured due to the extra power that is important for crucial KOs.
• Good, because it provides good coverage (Ground + Rock is pretty effective), specially against Ice types

As you can see, there's good and bad sides to both. The above answer tell why. Based on the rest of the information, you can choose either.

My personal suggestion? Try both for some time. Whichever seems to work better for you and your playing style, you should go with.

Answer 2

Probably Flamethrower. Assuming you have Dragon Claw or similar, there is almost no situation in which even a super effective Rock Tomb does more than a STAB Dragon Claw. A Fire move, on the other hand, gives you an answer to Scizor and Ferrothorn.

BUT, Fire Blast > Flamethrower for Chomp. His SpAtk isn't that great, you need the extra power. Fire Blast also isn't as inaccurate as the comparable moves of other types like Blizzard/Thunder, to where the power makes up for the accuracy dip in most situations.

Things get more interesting if you compare, say, Stone Edge to the fire move. Rock Tomb is just too weak to be worth it.