I have no favorites, here are a few chips and why I use them.

SILabs F12x: needed the speed and the internal RAM cut a chip off the project. Also in one case needed the 8 ports.
Philips LPC9xx: less than a buck which makes the ideal for farming small jobs out of the main processor.
Philips P89C668: the best priced derivative with 64k Flash, 8k RAM and IIC hardware.
Any derivative except Atmel: When price and performance fit the job.

I refuse to use Atmel because the Errata is years late.

Erik