We have stayed at the paris marriott and think its great. We build our trips around staying there. There is a marriott in heidelberg, but I don't think there is a Ren. We enjoyed it too, try to get a high floor water view. I'll be interested to hear what you think of the 2 Austria locations as we are planning on including them in next years trip. On your way to or from Austria to Heidelberg consider Munich. The Marriott is nice, and the new courtyard seems to have a great location, and if you paying for the hotel anyhow try the (non marriott) Platzl, right next to the Hofbrauhouse.