HI,
This is really an individual preference thing. I personally have a 2 light setup (Alien Bee's B800's.) I use one as a main light with a soft box, and the other as a backlight at times, or a fill light (depending on the shot.) I also use white foam board for reflectors. My studio space is approx. 12' X 14'.
This set-up for me acheives great, professional results. A softbox is going to soften the light. And although I prefer the soft box, umbrellas can acheive similar effects at a lower cost and more portability. What exactly are you going to be shooting?
I have only used Alien Bee's, so I don't have anything to compare them to. But if you search around these forums, you will find that 99.9% of the users that own AB's will praise them, and their customer service.
I highly recommend AB's!
Good luck in your quest.
Peac!