Not Choosing an MCU

Before I try and choose and MCU, I better try and figure out what I want the MCU to do. Basically, I want it to do as much as possible and I don’t want to have to add a bunch of extra hardware to build the application. From the LogStick requirements in my previous pos, I think I want the following:

• Some A/D to connect up the sensors
• A real-time clock.
• Lots of on-chip Flash to store the software and the logs. I guess want some kind of scalability here, I don’t really know how big the application is going to be so finding an MCU family with different memory sizes would be useful.
• USB connectivity to connect the LogStick up to the PC so it can dump its data
• A sleep or power-down mode when the LogStick isn’t logging
• Some on-chip RAM working area would be desirable
• A watchdog timer. Gotta have one of those for it to be a true embedded application. Well, I don’t write perfect code that deals with every eventuality, so having something that reboots the application if it’s gone bye bye is essential. (Visualize son banging LogStick on the concrete shouting. “It’s stopped working!”)
• JTAG debug, personal preference perhaps, but I think debug monitors and bits of wet string rather archaic these days.

Googling ARM Microcontrollers shows me that there are at least four manufacturers out there with ARM processor-based MCUs. Now which one should I go with?