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A Welsh Cob, they are better of with jumping, but that’s just my opinion.

anyhorse is cabable it all depends on how you train it, but i think a persuron are anthing of a similer stocky size would find it difficult. but im more in to showjumping so im not that sure.

welsh cobs are more jumpers than elegant dressage horses
treakeners and hanoverians are great dressage/jumping horses
freisians are more show horses
XD

Friesians are beginning to get a name in the Dressage world as they are now being bred "lighter" but this has not been always the case.

My Friesian is very "Baroque" looking but light on his feet. He is my dream horse, fiercely intelligent and we are learning together. He has good bloodlines, is papered and from Holland. I bought him because he has crooked ears.

You cannot get a better, more trusting horse in my opinion. Though very strong right now (he has been recently gelded) he is never aggressive in a mean sort of way. He actually teaches me!

Look at what you would like to do overall with your new horse. Do not look at your horse as a "dressage machine" (not to be too forceful here). I think that every breed on your list has strongpoints and in the end, how you bond/learn with it, will help you in competition. A horse that trusts you, will do anything for you including winning.

I will let the others answer you better concerning the other breeds.

Do lots of research before your purchase and ride many horses before signing on the dotted line.

I show fourth and Pre St George right now, and this is my opinion:
Any horse can do dressage in the backyard. It depends on the expectations you expect and what you wish to achieve. But if you are going to show at a higher level show, such as a USDF recognized one, the stereotypes and biased-ness is hard to ignore.
Welsh Cobs are thought to be little and unsuitable. Any sort of training will never get a pony to get the long natural stride that is prefered by the judges, and regardless of talent, a pony rarely ever recieves the scores it deserves.
Trakehner; I own one of these myself. He is ridiculously good at dressage so naturally, he has always been a good sucess. He is only a baby, but has completely proven all the stereotypes I thought existed. He didnt know anything at the point of his first show, didnt understand at all, jumped out of the ring, and placed high above people who stayed in the ring, simply because he is the correct "type".
Hanoverians are really well liked, but I think this trend will die out. They are being bred heavier and heavier, completely against what dressage trains, and overall generally adds to the work of training. Im not fond of them, but they are one of the most frequent.
Freisians are seen by non dressage people as a great dressage horses, but in the show rings, they are ignored. People still view them as carriage horses and I have not yet seen a high level one. (hey, freisian lovers, dont eat me, this is my personal experience)