The 300
I don't know much about the Sovereign, but I instruct on the CL-30 and know it pretty well. I'll brag on it first.
It has amazing range for its size. 3100 miles. It's dispatching at 99.6% reliability. It's surprisingly simple, with no LEDs, and no overhead panel. The Mitsubishi wing is very forgiving, having demonstrated steep turns at FL450 without eeking into either side of the coffin corner. It is rediculously quiet in the cabin as is, and with the Lufthansa Technik NICE system (cabin kit and soundproofing), you're looking at 56 dB in the back. The HTF7000 Engine had to be derated so the plane could make glide path, which is good for us, because it extends the life of the engine. The engine also has 50% fewer parts than the 731, with all the lube lines encased in the gearbox and right at 40 borescope points allowing for on-wing hot section inspections.
The bad news is that that the thing is still awefully new and fairly pricey. I agree with the other chap when he says you're likely to be looking at 16 million for a decent airplane. There are some snags with the AOG parts logistics, but again, it's dispatch rate is very high. The other drawback is that right now, it is a non-autothrottle aircraft, with that option anticipated later this year. The Collins FMS 5000 is currently not WAAS capable.
I do know that compared to the Citation X, it has been proven to operate at $1 less per mile.
Hope that helps.
RM