Agree with Glen's feedback, I did ME and MEI and MEII in a C-310-I, and don't regret a minute of it, especially after being an MEI in a BE76 for a year. The C310 is docile and handle-able yet requires some skill to be a ME, and makes you be a true ME pilot. I did a couple hundred hours in a C310, and after Glen goes through his as he indicates he is, would be a great bird!
At the same time, I agree with Steve; I had a chance to run a long-nose Aztec a couple times (with zero time flying this make/model prior to departure) a couple times that was a very nice, comfortable, formidable ride. Love those O-540 or IO540 engines as much as I did the IO4070's on the C310, and a very stable platform.
Oh a great 500B with RayJays would be my dream airplane near term, before of course a 690A with -10.
And also agree with Steve, the economics of ME training is not for the 6 cylinder world anymore. (too bad).
Flat out, love my C310 time as a ME trainer and runner, love and cherish my AC time I was fortunate to reap under Morris' mentorship, and enjoyed my "Aztruck" time as well.