First time river cruise for us. Had seen the commercials on television and we had always wanted to enjoy one. Emerald Waterways offered us half off and a drink package so we chose a 14 day sailing up the Danube starting in Budapest.
Random knowledge which might help you in your choice:
Ship sails under 2,000 bridges and goes through 68 locks on its way from Budapest to Amsterdam. A lot of traffic is on these rivers and will dictate how your trip will be (and of course if it is high water or low water level). One town we stopped in was cut short by 1 1/2 hours because we couldn't get through some of the locks during our time period.