IMHO if the trailer has no slides the 8' width is a better choice. Our Futura is 8' 5" wide and in the shopping process at the time we deliberately wanted a trailer with no slides. It's a little more liveable if you find yourself cooped up inside for a prolonged stretch of bad weather. When I go to RV shows anymore and check out some of the 7' wide models they feel a tad claustrophobic (and so do some poorly laid-out 8' units).
As far as seeing behind the trailer, get a good set of towing mirrors and you'll have no issues. Where maneuverability is concerned I can't say we've ever run into a situation where the width of our TT was the problem (and at 28' length is usually not an issue, either). Tunnels? A non-issue in my book.
All other things begin equal, my standard advice is to get the TT that has a floorplan that works for how you intend to use the trailer. Good luck!
