Being that I work with outboards for a living, I can tell you the difference.
A carb motor--if it sits a while, you WILL be cleaning the carb. The jets' orifices are so small that they plug easily. EFI? "Mostly" a non-issue. That said if they sit a while, like years usually and it doesn't run the next time you use it, you get to replace a fuel pump (the pump sock at the minimum) and possibly the injector(s). I've only had to do this twice, both on the same motor (115 yamaha)--both times it sat for 2 1/2 years between use. If it were carb'd, it wouldn't be any cheaper because there'd be 4 carbs to clean. If a 2 stroke V6, the passages are so big, that they may not have gotten plugged at all. That and most of them have a mechanical choke that helps jump start fuel flow through those jets.
You'll like the 4 stroke. Quiet, use very little fuel, throttle is more responsive, it runs exactly like a 2 stroke of the same HP. The days of them being sluggish are mostly gone. The newer stuff a lot of times will out-accelerate the old 2 stroke stuff. There's no smoke at first start. There's no mixing fuel. Maintenance is mostly the same with the exception of an oil change once in a while. Big deal. If you do any of your own mechanic'n, pick up a fluid evacuator and make it real easy, fast, painless, and no mess--And you'll find a thousand other uses for it too. Some of them might want you to put a timing belt on it every 100 years of use or something like that. Big deal. Most 4 stroke stuff is about half as noisy as a comparable hp 2 stroke. I frequent a small river that's pretty popular here and I always know when there's a 2 stroke coming around the bend. In the morning fog it's nice to hear it as a warning that they're coming so I can get out of the middle of the river if need be. I can hear them, usually, a mile away. With the 4 stroke motors about all I hear is the boat displacing water, unless it's a jet outboard, then they're a little louder...but if you've ever heard a 2 stroke jet....OMG!! Talk about noisy. Last week there was a guy with a 40/30 Mercury jet (2 stroke) that could be heard for miles. I was about 2 1/2 miles upriver and heard it coming. I thought it was right there. 15 minutes later it finally got to me, and another 15 minutes goes by before he shut it down. But that's a jet...they're all noisy, with the 4 stroke stuff (particularly Yamaha) being less noisy than their 2 smoke counterparts. The mercs are a little louder for some reason, maybe the exhaust in the leg is different.
The nice thing about EFI is it just starts without using a choke. If it's -20°F outside, you push the button and it's running, it's literally that simple. It is a little more responsive, particularly when cold. It runs mostly the same from stone cold to hotter than normal operating temperature. The throttle is more linear too, hard to describe but that's the best way I know to put it.
Like any outboard, the enemy is periods of non-use. Start it once a week if you're not going to use it even if just for a second, out of the water is fine, all you're doing is circulating some fuel through the system. Dirt dobbers have been a big mess here lately too, so if you can cover the cowling area with a garbage bag or something to keep them out, that's a good thing to do. Remember-outboards don't have air filters, so if those dirt dobbers build their nest under the cowling, and you don't get rid of them, that dirt nest comes apart and goes directly into the engine and at that point it doesn't matter if it's 2hp 2 stroke or 500hp 4 stroke, engine damage will have occurred. I recommend to many to pull the cowling off for inspection every once in a while just for this reason.