I should mention this is for our powder room.

Depends on your budget - there are many brands at different price points. I would suggest you go to a Ferguson's showroom and look at features and styles and price points. They would help you decide.

Thank you! Does the style of the toilet have to match the sink/vanity?

Style should blend with style of your home.
For traditional, I like the Kohler Memoirs.

http://houzz.com/photos/381229

These days it's best to find something you like and NOT match. Design style has moved away from matching things. But I would suggest you go for white as it will stand the test of time.

We used the Kohler Santa Rosa toilet in both of our new bathrooms - I liked its clean lines and the fact that it's all one piece.

Our clients prefer skirted toilets for ease of cleaning. Look to Toto, Kohler, Porcher or Durivat. Consider the height of the toilet as well as the flushing option, dual with buttons on the top of the tank or lever on the right or left.

Here is an example of a Toto Aquia dual flush skirted toilet, notice: no exposed trap to clean around.

Here is a Kohler Persuade dual flush skirted toilet.

Here is a Porcher one piece skirted toilet.

I can't have idea to my house with 8*8=64m2, please you help to me ,,, my mail hoangphan731@yahoo.com

We have the Toto brand at our new offices so I chose it for our powder room last year. Love it. White is a good choice and higher seat. Ours was the Ultramax II.

A couple of years ago I worked for a kitchen/bath designer. We had a Toto rep come in and he explained that his toilets are THE toilets for "high output" people. According to him, you can flush 25 golf balls at once and they all go down. Loved how he phrased that.......

Yes, I like the Kohler Persuade