What are the plus' s and minus's of these two trailer set ups? Does a triple axle have problems backing up into tight turns?

Yes in tight quarters the triple axle is a little tougher to manuever.

I personally prefer a triple axle. I think they tow nicer, better balanced, and like being able to strap an axle up and keep on going to the nearest repair facility should you lose a bearing or hub.

I agree the triple axle is superior to a tandem when pulling down the road. Better weight distribution, more redundancy if something goes wrong.

That being said, it will depend on the size of boat you are pulling. If you are pulling a 24' boat, the third axle is really not needed due to weight and dragging the third set of tires is over kill. Most trailers I have seen start using triple axles at the 29' range, but, this will depend on weight of the boat.

Of course all this can be trumped by using tandem, duel axles. (10k Axles+) They will have the redundancy factor, better turning and stability due to the bigger tires and width... I have only seen these trailers set up as a gooseneck hitch, which will also add stability.

Had both, really don't notice a difference backing up or turning. The center wheel will kick up some stone when backing up but that's about it. Depends on the boat length/ weight if you need it.

I would go with as few as possible axles. I have had both and I would go with two heavy axles vs. three lighter duty axles. It gets you out of the "trailer tire" relm into the LT world which I have found to be much more reliable. Also less bearings, breaks, hydraulic lines, etc....

I love my tandem dually. I don't think I'll ever own another triple.

Count me up for triple... I have trailers that are 1,2 and 3 axles. The single sways a lot, the tandem (box car hauler) sways less but still sways and the triple is solid as a rock. Disk brakes are on the front and rear axles.
Some other thoughts, the triple has more tires on the ground, so if you hit a pot hole or a ditch it is more forgiving than others. As stated before you can strap up an axle if you have a problem. But the down side is that you do have more tires and hardware, your back tires will scrub in tight turns and it has to be level going down the road.
What are you going to be putting on said trailer and where do you boat?

I have both now, I like the heavy duty tandem better with the bigger tires, but the triple does seem to float down the road better.

My only concern is don't get a trailer with too much suspension, the less weight on a heavier trailer makes the boat ride hard you need a balance of weight carrying vs load so the trailer floats like an old Caddy running down the road, that's your goal to float!

Boat is a old 28 Pantera that is pretty heavy. Boat has speedmaster drives with their transmisions and is built heavy, way heavier than my 99 was.

Its its simple really if you trailer long distances, frequently, there are some that travel 100+ miles every weekend to go boating, u want a triple, if you trailer alot locally and jack it alot you will love the tandem, I have a tandem under my 30ft boat and I would be curb hopping every time I go in and out of my driveway with a triple, just make sure its setup properly