If you are on a budget, then purchase the 1.5GB one. If you aren't on a budget then why not purchase the 3GB one?
you know,in my country Phantom is cheaper than MSI lightning,I am on a budget to some extent,,and here for gtx 580 or many other components we should pay 100$ or
more than their real prices,if in the USA someone for example buys gtx 580 just 500$,we buy it 600$ or a little more. but I should check the MSI Xtreme edition price as it has
3GB VRAM and has been overclocked better than its rivals. Did you know that the GAINWARD GTX 580 Golden sample is slightly stronger than Phantom??? http://www.rwlabs.com/article.php?cat=&id=325&pagenumber=5http://www.fudzilla.com/reviews/item/21800-gainward-gtx-580-3gb-phantom-tested