I think Rypherior is the best of the three, but what do you guys think?

Definitely Magmortar. It learns the best moves, it has the best stats (not by much, though), it has the least type disadvantages. Rhyperior is quite easy to beat, being very weak against water and grass, while also being weak against ground, fighting, ice and steel. Magmortar is weak against water, rock and ground, but can offset two of those disadvantages by learning thunderbolt and earthquake

I would have to say I prefer froslass rather than the other two.

seriously? it is much weaker than the other two

I say Magmotar because it looks really cool.

I say Magmortar because it has less weaknesses than the others, it looks very badass, and it has some great stats. Plus, Flint(in Pokemon Platinum) uses Magmortar, and Flint is cool.

I say Magmortar, it doesn't have too many weaknesses, no MEGA weaknesses like Rypherior has. It also has good stats, learns good moves, and it was one of my best Pokemon in Pokemon Platinum. It was Level 83 with Heat Wave, Fire Blast, Fire Punch, and Overheat. Froslass didn't really have a good type. It was weak to too many types for me. So Magmortar is my pick.

I choose Rhyperior, Rhydon was always my favourite pokemon until 4th gen, Frosslass is a PAIN to get and Magmotar is cool to but Magmotar doesn't cut it for me

Magmortar all the way, but I always pick the fire types.

I'd have to say that I prefer Froslass. Ghost and Ice together? AWESOME! Yes, it does have many weaknesses. But with the right moves, right strategy and right training it can be awesome.

I prefer Froslass, even though it is weak to Steel, Fire, Rock, Ghost, and Dark (compared to Rhyperior's quad weaknesses to Water and Grass as well as weaknesses to Fighting, Steel, and Ground), which is actually the same as Rhyperior's weaknesses, minus the four times weakness to Water and Grass.
I suppose Rhyperior is the best statistically, but I hate the way it looks. Just in my opinion, but Froslass is far cooler and mysterious.
Just noticing, but so far all of the girls here (all two of them. Hurray for AdorableCookie for not making me the only one) have picked Froslass, while all of the guys picked Rhyperior or Magmortar. Hmm...
And for those saying Froslass is a pain to get, Rhyperior and Magmortar are impossible to get unless you have multiple Magmarizers or Protectors, two DS's and two copies of the Generation IV games.
EDIT: Noelia picked Froslass as well... This is actually getting funny.

I voted Froslass, it's better than the others and he has less weaknesses.

magmortar since i like fire type pokemon

I will say Rhyperior because I think he's too cool.

Frosslass, good bye to Rhyperior, he's out of the question. However just you hypnosis on Magmortar and just go Dream Eater on it.However Magmortar can use fire moves and get rid of Frosslass, you'll never know what moves Crono taught it, Nyah.

Froslass is awesome. Froslass has the ability to freeze foes with her cold, chilling breath and create illusions to manipulate both her prey and foes.

But, I also like Rhyperior. Rhyperior can insert rocks and boulders into its arms through holes in its hands and then fire them like bullets. They are monstrously powerful and are massively difficult to take down.

But, I would give Magmortar my vote. Magmortar can also use Thunderbolt, Earthquake, SolarBeam, and Rock Slide, which can help it to defeat Pokémon which it is weak to.

I say Magmortar because he can learn attacks that are super effective against rhyperier and frosslass. also because fire pokemon are my favorite.

Jeez, did no one play Pokemon Platinum? That Froslass could kill just about anything. But i spose that was just my problem then. I voted Froslass.