Gate first seems to make more sense from a foundry perspective, since it can be integrated into an existing process line without too many changes. The foundry business has to focus on integrating the needs of many different clients and products, not just one (like microprocessors). Low-cost integration across a product group is essential for success, otherwise equipment and production costs will eat you alive.
Here again TSMC seems to have a upper hand by following the footsteps of Intel. As Intel has shipped two generations of high-k dielectric based processors so the technology is proven. Only after AMD ships its processors, we will know which technology is better and has a smooth road ahead.
Atom, of course, also targets handhelds where very low power is a must. Todate, though, Atom is still made with the 1st generation 45nm high-k process. It'll really start getting interesting when it comes out on the 2nd gen 32nm & 3rd gen 22nm processes
Intel's high-k process, if I recall, has many extra process steps and complexity, including dummy polysilicon gate removal, and multi-metal deposition. Even so, it became a high-volume process. Yet Atom still consumes too much power for some. It will be interesting to see AMD gate-first vs. Intel gate-last CPU benchmarks.