Golurk
- Excellent Attack
- Iron Fist is a good Ability
- Learns moves like Shadow Punch, Earthquake, Close Combat and Heavy Slam
- Ground Ghost is pretty solid offensively
- Evolves pretty late
- Doesn't get many physical Ghost moves
- Lots of weaknesses
- Lowest Attack of the three
- Very slow and a bit weak defensively
Mamoswine
- Second-highest Attack stat
- Ice/Ground is amazing offensively
- Thick Fat is great if you can get it
- It learns moves like Earthquake, Ice Shard, Iron Head and Stone Edge
- You need a Move Reminder for Mamoswine
- Slow and not the best in the defense department, but better than the other two
- No good physical Ice moves unless you breed one
Excadrill
- Highest Attack of the three, with a whopping 135
- Steel hits those annoying Fairies
- Evolves at a good point in the game
- Learns moves like Earthquake, Iron Head, Poison Jab, X-Scissor, and Swords Dance
- Faster than the other two
- Mold Breaker is nice if you can get it
- Frail, but it does have a solid HP stat
- Drilbur is not the greatest
I think you need the Steel coverage a bit more than the Ghost or Ice coverage, so Excadrill is the way to go. It's fast, strong, and learns excellent moves that can help you all through your journey. Mamoswine is a close second though, and while Golurk works, it's the worst of the three.
Excadrill @ anything
Ability: Mold Breaker / Sand Rush
- Drill Run --> Earthquake
- Metal Claw --> Iron Head
- Poison Jab / X-Scissor
- Swords Dance
Hope I helped!