Hello.
I am currently USING a Radeon HD 3870
http://www.gpureview.com/show_cards.php?card1=&card2=547


and i am comparing it to a GTX 250

http://www.gpureview.com/show_cards.php?card1=606&card2=547



I have herd alot from people saying which card is better or i should buy this instead of that, but my question is why? It seems like a simple question but no1 is ever ABLE to answer it.


Ultimately my question is.. What makes a GFX card better to another. What is important. Bandwidth or core clock? what are these things. BASICALLY im looking for a site or guide to tell me what is more important when it comes to all GFX cards and how I should weigh each aspect of a card.one thing I see is Radeon HD 3870 has a 256-BIT GDDR3/GDDR4 memory interface, while GTX 260 (You listed GTX 250 but nvidia.com lists only GTX 260) has a 448 bit memory interface.

Also you know that the nvidia's can do the physX if you want those ...
The GTS250 is a lot better than the HD3870.
Between different MANUFACTURERS (e.g. ATI and Nvidia) or major lines (e.g. Geforce 7 series and below vs 8 series and above) there's no easy way to compare.
Comparing clock speeds and shader counts will not give you anything meaningful. In pure shader count the ATI cards dominate, but their performance doesn't live up to what you'd expect from just counting shaders because of the design and the difference to Nvidia cards.
The only way to see what card is better is to look at benchmarks from a reputable site, or ask someone that knows.