The 310 isn't a difficult airplane to fly. Although I don't particularly recommend it as a trainer, many people use it as one, and it does make a fine first twin. With any twin, proficiency is key to safe operation. There are actually various sim schools that exist that offer 310 classes. Insurance won't offer you a discount for it (at least, mine won't), but I am considering doing it anyway in spite of my 1600 multi hours (400 in 310s) because I do believe it offers some good benefits, specifically being able to simulate things that would just be too dangerous to attempt in the real plane. V1 cuts, etc.
When I bought my Aztec, I pretty much stopped flying any other plane for the first year, mainly to help build my multi-engine proficiency. I recommend this path for anyone who is transitioning to twins. For most who buy their own, I think this is reasonably simple since it seems most people will buy their twin and that will be their only plane. Now, with the 310 as the only plane I have immediate access to, it is the only plane I will be flying anyway, and I'm happy with that. I did not like the daily flipping between the 310, a 310R, the Aztec, two Navajos (one -310 and one -350), the Cheyenne, and the Commander. It doesn't do well for proficiency in any of the aircraft, does provide for confusion swapping between aircraft. The 310 doesn't have cowl flaps, but the Navajo and Aztec do. The Cheyenne and Commander are turbines, but one's PT6 powered and the other is TPE-331 powered, both of which have completely different start procedures. 310 has electric gear, the rest have hydraulic. Etc. etc.
My experience with 310s is limited to the N I fly and a couple of Rs I've flown (the RAM T310R and a Bearcat R). I like flying the N better as it has a much sportier feel than the Rs. Even the Bearcat R with 300 HP IO-520s I found to be a real dog off the line with two people and full fuel on a cool evening compared to the N I fly with 6 people and luggage (max gross) on a hot day. But the R has better support, more STCs, is newer, and has a bigger interior (plus nose baggage). The older 310s are even faster than the N, although the one I fly is slowed down with VGs and boots, but sped up with a Colemill conversion that gives it 520s.
Barons are faster than 310s for the same power, but that's because their frontal area is smaller. This translates into less space between you and your copilot. If you fly solo up front for the most part, I wouldn't think this to be a problem, but it would be an issue if you have copilots who aren't small. Having flown in various Bonanzas/Barons with clients, none of whom were overweight (and I have the waist of a string bean - even with my wife's excellent cooking), I always found myself wishing I had the extra space of the Aztec or 310. I guess I'm spoiled.
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