I've used various softboxes over the years and to be honest the "good" brands are all pretty comparable these days as the expensive ones seem to have got cheaper and the cheap ones more capable but expensive. When I swapped my lighting over to Bron it was at the time of the release of their latest softbox range. What started off as getting one to try ended up replacing all my softboxes as I was so impressed. Quality of materials and construction is first rate, excellent stippled silver interior, great quality diffusers and benefit from the ability of getting a third outer diffuser that works very well and Bron also offer a grid for each in the range.
The new range can be adapted with speedings for many different manufacturers and as you also use portable flash, Bron do a speedlite adapter also.
Size and shape is all very personal and can depend on the quality of light you require. Big octo's are great but not very portable and a pain to set up many times and while smaller octo's are nice they are not very soft. I like rectangular softboxes and one of my favourite is the 60cm x 100cm for its compact size but good softness close to the subject. The collapsable umbrella type beauty boxes also look interesting for a cross between a softbox and beauty dish. Not tried one yet but will love to try one out.
http://www.bron.ch/broncolor/how-to/shoot-this-photo/showproduct/softboxes/beautybox-65/?cHash=1688f2c27e50e4b3c0d37727ceaa0950#.VgHNULTG6EI
Its hard when you love and use one lighting brand to see past what they offer but I do feel the Bron softbox range is excellent and not just for Bron users IMO.