I like the Castle SW4 combo. I have the 3800kv on my Slash 2wd, and it's very smooth, quiet, runs cool, and modulates well at low speeds (minimal cogging as well). If I were to pick a new combo for my 4 Tec 2.0, it'd be the SW4 3800kv (still running the stock brushed Xl-5 and Titan 12T). Castle also offers it in the 5700kv, but that's too fast for me, and I like a bit more bottom-end torque for drifting.
Hobbywing also makes nice motors and ESCs, but I've never found their products to be as refined as Castle's. I have the XR8 (sensored brushless) combo (3660 4300kv motor) for my Slash 4x4, and even in sensored mode, it has issues going from forward to reverse and vise versa and isn't as smooth as I hoped it to be.