Kirk,
Both of those brands make great products and you'll have no problem baking bread in a "pizza" oven (aka a round oven), but baking pizza in a vault style oven is much harder. "Bread" ovens (vault style) are designed to hold a much higher thermal load, so they're traditionally fired to a lower temperature for a longer period of time. That allows a baker to make multiple sets of loaves from the residual heat that the oven puts out. Pizza ovens are quicker (but still not super fast) to head up and are traditionally fired at higher temps. A round of breads is totally doable, but unless you refire after that, the temps can be a bit tricky to manage. Still, unless you're planning on baking a ton of bread (well more than you can eat), just get the round oven.
One thing I might consider, if I were you, is building a earth/sand oven (not straw) first, to get a handle on what you're looking for. I know part of the reason that you're inquiring about these ovens in particular is that you probably don't want to build your own, but assuming you build the base properly (or have it built) you can re-use it for your refractory oven once you buy one.
The advantage of starting off with an earth oven is two-fold. They fire quicker (and at a slightly lower temp, to be fair) but mostly it would allow you to figure out what size oven you need, for a very low cost.
Oven size is one of those things that depends entirely on your cooking habits--there's not a best size, really. Bigger ovens look great and can hold a lot for parties, but they also take longer to fire. If you want to use your oven often, having a smaller oven that can get up to temp quickly might be better than a larger oven that you can only use on the weekends. On the other hand, if you work from home/entertain a lot, then a bigger oven would let you do more with a single firing and would really be a workhorse at a party (ie you can crank out pizza and some other things all at the same time).
There are some great instructions on building clay ovens out there (river cottage produced one which is helpful) if you go that route. It looks to be pretty easy, though the labor is spread out over several days, so there's that.
Hope that helps and good luck!
