So I just ordered a Nexus S, but I've been having second thoughts. All of these dual-core phones are coming out, and I'm wondering if I should have waited or maybe gotten the Atrix. Thoughts from Android vets?
The Atrix isn't the greatest of choices. Yes, it has a lot of features, like the fingerprint reader, additional accessories (laptop and multimedia dock), "4G," etc. Sadly, it's not the most responsive of phones, despite the dual-core processor. The additional layer of Moto Blur and AT&T's bloatware makes for a pretty laggy experience from what I've heard.
Now T-Mobile's G2x is a pretty sweet choice, but it supposedly doesn't work on AT&T's 3G/4G network, despite the original specs on T-Mobile's site suggesting so. I'm assuming you're on AT&T, so this really wouldn't be an option for you.
I'd say the Nexus S really is the best choice on AT&T right now, and will be until the Galaxy S II is available for AT&T's network. Considering the way AT&T likes to nurf phones, the Nexus S might even remain a better choice than the Galaxy S II.
In terms of processor performance, the Nexus S really isn't all that behind the latest dual-core phones. It's missing that extra thread for general CPU stuffs, but most instances where you need additional power actually comes from the GPU. The Nexus S' SGX540 performs decently close to Nvidia's ULP in current Tegra 2 phones. The SGX540 actually handles textures better than the Tegra 2 GPU, though Tegra 2 wins by a fair margin with polygon performance.