I personally am quite happy with the ride. Keep in mind that many factors can influence ride quality more than frame material. Tires play a big part. As for the Thudbuster it is definitely worth the money to me. I have a couple of them if that is any indication of how much I like them. For what I've invested in Thudbusters I could have bought another nice bike.
I went with the aluminum frame as I think it saves a couple pounds and Peter assured me the reliability would not be an issue. Both frames have the same warranty.
As for gearing I like having something down around the 24" range for when I am fully loaded and on the steep climbs. It is still faster than walking (if not by much). Obviously this is a personal as well as environmental choice. For me I'd rather spin than stand on the pedals. It is easier on my knees and most folders don't like all the stress you can put on them by standing up. You get a lot more leverage (on most folders) with the long stems up front and this can exert a lot more force on components. So I have adopted the sit and spin method on steep hills. I choose an appropriate gear to allow me to do this.