Compare width, too. Some 17' TT's are narrower at 88", supposedly to be easier to see around. Also compare black and gray tank sizes - some are 25 gallon.
I found moving up to an 18' was a bigger difference than just one foot longer on the models I was comparing.
I ended up with a Shasta Oasis 18BH that was 96" wide. Can see around it just fine, and those extra inches make it a bit easier to turn around in the bathroom :) I was happy with the size of the tanks, too.
2016 Shasta Oasis 18BH
Dry Hitch Weight 349 lbs.
UVW 3,144 lbs.
GVWR 3,830 lbs.
CCC 686 lbs.
Exterior Length 21' 9"
Exterior Height 10' 5"
Exterior Width 96"
Fresh Water Capacity 42 gal.
Gray Water Capacity 36 gal.
Black Water Capacity 36 gal.
Awning Size 12 ft