Our first camper was a brand spankin' new '07 ROO 23SS and it was the perfect one for us at that time. Yes, you do save some weight IF you are considering a HTT and a TT of the same size being towed down the road....not the opened up size. Our 23SS was actually more like 20' and a smidge when closed, but opened up we were very close to 30'. Re storage, totally depends on the model. A 30'opened up HTT will likely have less storage than a 30' TT, but we tend to load up more than we actually NEED and still had plenty of space. We loved everything about the HTT, the open feeling, the layout, ours had an awesome kitchen and a small, but acceptable bath. What with one thing and another, in '13 we made the move to a TT...26'. It was also the perfect change for us at the time. We lost our large kitchen, gained a great bathroom, gained a real bedroom, gained a nice living area.
Remember that you're going to have to deal with the frontal drag with either and 10 mpg is reason for celebration at the end of the day, regardless. Suggest you do some online searching, some in person looking - try to ditch the salesman, and make a list of things you must have, would like to have and don't care either way. Think about how you camp, things you would likely haul with you and for sure, do a thorough check on your tow vehicle and its limits. Then subtract about 1000# for wiggle room and you'll be in safe range.
Happy shopping and happier camping. Either way is great!