Huge bonking subject. For one, I know a dude named Todd Bailey who has serious homey relationship with Atmel. Also mainy other products suchs as Arduino have been made with Atmel, which is considered to have the more "old-school" style.
Also dudes such as Todd Bailey and Karl Ekdahl will point out the benefits of both, and in the end may frowningly celebrate some virtues of the PIC. The frown is because the PIC is kindof like being in "boy scouts" in that it is somewhat metrosexual.
But bit banging can be implemented in both. Homeys will also say that a true man programs in assembly, running these robot as an extension of ones own intellect. Homeys will also point out that c is great to s-ketchup a design real quick.
I personally have decided to make something wonderful in assembly language. It will be called "Chub-Lisp", and it is an 8 bit computer music language that runs on an embedded...
Microchip PIC 18F!
Here's the deal. Atmel is really cool especially for being like Spock. I'm sure the data sheets are logical. PIC is like being in Pudding Lane on London, with brick alleyways, the data sheet is long and has its own language.
But learn these winding roads, and use the services of the farrier, the blacksmith. These "meta-silicon" homies will do lots for you for cheap (i.e. in a only few clicks of the tock), like send bytes out USB.
Or Hardware Multiply, which places the PIC18F25J50 in the unique position of running a lot of 8 bit DSP, such as computer music programs! It gives it a unique sound, that starts out with my friend the Muslim Ice Cream man, and his chiptune sound unit, but extends into the wild lands of Computer Music, resonances, pluck, granular synthesis.
A squishable ice cream truck.