My best advise is to go rent each of the HD touring bikes and see which one feels the best to you. They each use the same frame but as you note the Street Glide is lowered and basically a Road King with a fairing. The difference between the Ultra or EG and the RG is the fixed fairing on the RG. For me the answer to what was the best fit for me was the RG by a long shot. It handles unbelievably well for a big bike, you just have to ride it to see. As far as the use or enjoyment of the stereo you will be able to hear it on all of them. Just one thing pay attention to how the bars are set up on the bike before you take off on the rental ride (and I suggest you do a full weekend with each bike). The dealer will adjust the bars for you to get them in a comfortable position if need be. Also sometimes the dealers will have similair looking bikes in their rental fleets but they have different bars on them. Pay attention and look to see if the bars are the pull back bars or not. For example I rode an Ultra with pull back bars and hated it but liked another Ultra without them. The pull back bars just put my hand position too close to me than I needed. Another thing, look at the list of equipment that comes on these bikes standard. Go to the HD website and print the lists and compare. You will see the Ultra comes standard with some more equipment than the EG or the RG, being the CB/Intercom and Ultra tourpack , etc. They are all great bikes you just have to find the one that suits YOU the best. For me it was the RG but it will not be for everyone. Let us know which you liked after you ride them all. Hope this helps.