It all depends on what you can find, what your budget is, and what you're willing to deal with.
I got an 8 lug semi-floater and a matching front from a 3/4 ton truck. Since I was getting larger tires anyway, and got the axles for such a good deal, it was an easy choice to just get new wheels and bolt everything in. Semi-floaters are plenty strong enough for all but the largest tires. If you have a 6 lug front, you can readily find 8 lug hubs to make everything match, as the corporate 10 bolt front axles are the same.
Semi-floater 6 lug axles are desirable, but will almost certainly be more expensive, and depending on which one you get, may require relocation of spring perches. They will be from newer trucks and vans, so you have to pay attention to axle width as well.
Full floaters are tough, readily available and inexpensive, but pretty much mean you're going with 8 lug. Parts for them are cheap. The main disadvantages are that they are very heavy, and if you aren't running big tires ground clearance with that massive differential can be an issue. However, that's an axle you'll never need to worry about unless you're going monster truck big.
I've seen a lot of people that for some reason have an aversion to 8 lug axles, either because they don't want to change wheels or front hubs, but IMO it is usually a much simpler and more economical route. Unless you've got thousands tied up in your wheels, I guess.
