From tech. points of view, ATI has better technology than NVDA. However, NVDA is a market dominator. Never underestimate market power - NVDA up $5 last week after Q report. Sure, lots of NVDA fans.
Did you check news today? --
Merrill Lynch on Semis : There hasn't been much that has been able to stop the semiconductor stocks this year, but a call out of Merrill Lynch today is apt to slow the momentum of at least five of them. The stocks in question include Intersil Corp. (ISIL 21.02), Maxim Integrated Products (MXIM 40.61), Semtech Corp. (SMTC 17.77), NVIDIA (NVDA 20.77), and ATI Technologies (ATYT 6.80)-- all of which were downgraded to Neutral from Buy.
Good trade...