At the moment ATI is offering some pretty amazing feature rich products at a good price. The 5xxx series simply rocks. I bought myself a 5770 Radeon and i am very very satisfied with the card. The IQ is great as always with ATI, the performance is quite good and best of all the card is very quiet and power efficient. Of course the 58xx series is even better(faster) but it all depends on your budget, for my budget the 5770 was the right choice. I also bought a new mobo, ram and cpu, this time i completely ditched Intel and went with a Phenom II. Again AMD offered great price/performance so i went with that instead of i5 which btw is also a very good choice. The thing that really got me to switch to AMD was not only the price of the cpu but the prices of those mobos. I am planning to run CrossfireX with 2x 5770's and amd mobos with good Crossfire support(talking dual 8x8 slots, Intel p55 are usually 16x4 except the more premium ones) are cheaper than the Intel equivalents. So i got myself a Phenom II x4 965be with a nice Crossfire Asus mobo(amd 790 + sb 750 chipset) and 4gb's of fast ddr3 1600mhz ram. I am very satisfied with the new components, they work brilliantly.
As for your other questions. No Nvidia is not better than ATi and no ATI is not better than Nvidia. They are companies that make graphics cards and sometimes one of them has a superior product on the market and sometimes the other. ATM ATI has the upper hand with the 5xxx series cards.
Same with Intel vs AMD. Intel is currently the speed king but AMD is kicking back with some amazing price/performance products.
So to sum up, if you're not on a tighter budget go with Intel, otherwise go with AMD. As for the graphics card go with ATI as i can't recommend anything else than the 5xxx series right now.
Asus, MSI or Biostar ? All of them make good mobos, currently MSI is getting some very good praises from the hardware enthusiast crowd so they are definitely recommended. Asus is Asus and they are not the nr.1 seller of mobos for no reason, personally i prefer Asus mobos to anything else but it's just a personal preference, like i said MSI mobos right now are also very very good. Biostar is decent but the other two i think are just a little better.
