If you are getting the tube at the end of the journey then the quality of the fold, in terms of speed and ease, and the portability of the bike when its folded counts for more than the ride. 8 miles isn't a hellish long ride on any bike, you'll be fine on a brompton or a birdy, but wrestling to fold your bike as the train pulls off into the distance isn't too pleasant a prospect.
Its the speed of the fold that really should be the deal maker, some, like the Brompton or the Birdy fold in under 10 seconds, some take a minute or two (and in rail commuting terms thats an eternity as other passengers are tripping over you in rush hour, 4 times a day), some can take half an hour to get them down to a small pack size.