Both the Aztec and 310 are going to cost you the same per hour to operate, so the 310 will save you about 12% operating cost over the span of your mission, plus a 310 is way cooler than an Aztec. Seriously, my 310 was the only plane I've been in that got the FBO hottie out on the ramp to tell me I had a sexy plane. Personally I also prefer the IO-470 Continental to the Lycoming for multiple small preferences such as parts costs and general smoothness, but more importantly I like the Continental Fuel Injection better than the Bendix. Not only is hot starting a Continental a simple affair, it has an electric high boost pump setting that will keep the engine delivering power if the engine driven pump fails. The only thing you have to always remember is to not switch to your aux tanks until you have burned an hour out of your mains. Outside of that, the 310 has no nasty system surprises, and it runs a mechanical/electricical landing gear system rather than a hydraulic which I prefer. The key thing to inspect on the gear is the actuator torque tubes in the main gear wells. They develop a radial crack by the crank tabs, and when the crack finally splits, the gear doesn't lock down. There was a point where a good few of the twin Cessna fleet were grounded over this and the lack of replacement parts supply from Cessna, but it's my understanding that the issue has been rectified, and a higher quality part is available.