Im thinking bout buying in HDTV just to play my 360 on. But the one thing that I don't get is the 1080p ect. Is that the amount of pixels, is the higher the better or low stuff like that?

This picture explains the resolution differences pretty well. The red box is SD, while the green and blue are 720/1080 HD. Your TV has to stretch the image to fit it on your TV. The picture looks a lot better if it has a bigger image to stretch out vs a smaller one.

The higher the pixels, the better the image quality. I first started out playing my xbox 360 on my SD-TV. I then got the VGA cabled and played it at 720i on my computer monitor. There was one hell of a difference in image quality.

It is the number of pixels on the vertical. The actual resolution is 1920x1080 or 1920 pixels wide and 1080 pixels high. 720 is 1366x768 it has something to do with the TVs ratios

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A common resolution used in HD Ready LCD TV panels is 1366 x 768 pixels instead of the ATSC Standard 1280 x 720 pixels. This is due to maximization of manufacturing yield and resolution of VGA, VRAM that comes with a 768 pixel format. Hence, LCD manufacturers adopt the 16:9 ratio compatible for the HD Ready 1080p standard.

Not to poop on the thread, but I personally think that contrast ratio nowadays for HD sets is one of the biggest factors for image quality.

That really only applies to LCDs though. Plasma doesn't really have a problem with contrast ratios. The problem is there doesn't seem to be an industry standard definition of contrast. For instance my TV claims a 3000:1 I have seen some with 10,000:1 and other with 500:1. 500:1 would seem awful as all you could ever get is a dull gray never black. And yet I have seen Sony Bravia Plasmas claiming only 8000:1 whic would mean the LCD claiming 10,000:1 should have an even darker black than a plasma which is damn near impossible.

I think tis will explain it better. http://www.practical-home-theater-guide.com/contrast-ratio.html

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Conclusion: Numbers are there to impress and help selling the product but quoted peak contrast ratings do not really give you any information on the video projector or display device ability to render images with lifelike gray scales and colors - rather the only information that contrast ratio can deliver is how much brighter the 'whites' can be than the 'blacks'!

Indeed, I had to get in a lengthy discussion with my friend about the matter just a few weeks ago and he didn't seem to understand the issue with contrast ratios and why a 1000:1 isn't necessarily better than a 500:1. Ultimately your best bet is to go in to a store and see the displays for yourself.

Which is better 720p or 1080p?

1080p is a higher resolution, so naturally it will have a higher quality image. However, that only applies for video shown in TrueHD format, i.e. some video games and movies on Blu-Ray. In general, you're fine with a 720p tv under 37".