Frost Rotom Vs. Mow Rotom?

Question

Which one is more usefull?

Answer 1

Mow Rotom

Mow Rotom has 2x weaknesses against 4 types, this being against Poison, Bug, Fire and Ice types.
Mow Rotom has resistances against 4 types, this being against Steel ½, Water ½, Grass ½ and Electric ¼.

Frost Rotom has 2x weaknesses against 3 types, this being against Fighting, Rock and Fire types.
Frost Rotom has 3 resistances against 3 types, this being against Electric ½, Ice ½ and Flying ½.

On top of this Frost Rotom is damaged more by Stealth Rocks than Mow Rotom. Frost Rotom will lose 25% of it's max HP each time it switches in, compared to the 12.5% that Rotom Mow will lose if it switches in when Stealth Rocks is on the field. Rotom Frost is also vulnerable to the common priority moves Mach Punch and Vacuum Wave.

There's a reason why Smogon put Mow Rotom in the RU tier and Frost Rotom in the NU tier in Gen V.

Additional Source: Rotom - Bulbapedia

Hope I helped :)

Comments

Smogon doesn't put Pokemon in lower tiers, that's determined by the overall player usage percentage of that Pokemon. They can get banned to higher tiers due to being too good and or demanding a counter on most every team. But to add to your defensive insight: Rotom Mow gets stab against 4 types: Water, Flying, Rock, and Ground types. Rotom Frost gets stab against 5 types: Water, Flying, Grass, Ground, and Dragon.

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It isn't just their usage that defines which tier their in, it's also their overall potential.

Answer 2

All forms of Rotom can learn the same moves, albeit Hydro Pump, Blizzard, etc.

It all comes down to the typing.

Rotom-M has 4 weaknesses to Fire, Ice, Poison and Bug.
Rotom-M has 3 resistances to Water, Grass and Steel, and a x4 resistance to Electric.

Rotom-F has 4 weaknesses to Fire, Fighting, Ground and Rock.
Rotom-F has 3 resistances to Electric, Ice and Flying.

Type-wise, Rotom-M is much better due to Rotom-F being weak to 3 common types (Fire, Fighting, Ground) and Rotom-M has a 4x resistance over it.