depends on the trailer width.  I had a Lakota ( 6'9" wide) w/ 60/40 rear doors and while there was more room for the horses it really cut into the space in my tack area.  the horses are perfectly capable of getting in and out w/ 50/50 doors.  I'd rather have more room in the rear tack.   since that trailer didn't have pull out saddle racks it was very cramped. 

new trailer is 7'6" wide and what a huge difference.   it has either 60/40 or 55/35 (?) doors but there is plenty of room in the rear tack.