The size and shape of the softboxes you get is typically depemndent on how you plan to use them. Regardless of what you get, here are my observations and recommendations on softboxes in general:[list][*]I prefer a softbox with an inner baffle. It cuts down on the center hot spot.[*]If you're planning to use an egg crate grid at some point, it's MUCH easier to attach it to a softbox where the white front cover is recessed. Many cheap softboxes on eBay have non-recessed fronts, so it's difficult (but not impossible) to attach the grid[*]If you're planning to do a lot of location shoots, make sure the softbox is easy to assumble and sturdy enough to hold up over many shoots. Some of the softboxes on eBay are made of thin plastic which can rip and tear easily.[*]Some softboxes have inner reflective panels that can be changed from silver (or white) to gold. It's a nice touch if you do a lot of "golden light" photography.
I have two 20-year-old Broncolor 32"x32" softboxes -- made of durable canvas. Since I got them as a gift I don't know what they cost. I added a center baffle to each of them last week (glad mama taught me how to sew). I also have a cheap 36" x 48" softbox I bought for $20 on eBay. it's made of plastic, so I never take it on location. In a project that took me several hours, I managed to attach an egg crate grid to it last year. Now I never take off that grid!