We will have most of the day to drive from Eltz Castle to EuropaPark. What do you think is the more scenic drive with the nicest towns along the way? Moselle or Rhine rivers?

This would be just to make the drive more interesting. We wouldn't have time to spend any time in any of the places outside of quick stops or lunch. If no stops, the drives for both are about 4.5-5 hours. We also don't have to be at our destination by any specific time, just going to the hotel prior to the next day at the park. This will be at the end of July.

I think the scenery on the Moselle is better in some ways - the train line is not in the way of your views like on the left bank of the Rhine (if you are on a cruise it's less of a problem). But I like the towns on the Rhine better. The towns in the Moselle are a bit sleepier, the Rhine is busy and vibrant. You might just miss the Rhein in Flammen festival ('Rhine in flames'), which is 6 July this year.

How were you planning to drive? The fast roads will go past the Rhine, going south-west on the Mosel will take you into an area where the roads are just not as good or as fast (Trier for instance, if you get there, is a bit isolated, transport just isn't as good there).

Lavandula

Drive neither, you are in a tin box, you can't hear anything or smell anything, while the visibility is contrained by the metal around you.

The Rhein road is pretty fast, but you can take the parallel road which is faster
The Mosel road is pretty slow, and much prettier.
both have places to stop and have a coffee

I would have thought the Mosel takes you way off course for Europa-Park.
The Rhine route can be busy and I don't find it especially scenic, the railway gets the best bits, but there are plenty of places to stop and enjoy along the way. It will take you a good 6 hours of driving in any case if you stick to the Rhine.

Sleepier towns on the Moselle? Does that mean less touristy?

I was last there about 30 years ago, but I did find the Moselle prettier, and yes, pleasantly sleepy.

No less touristy I fear. The Mosel in summer is as busy as anywhere, and lined with campervans and RV at every opportunity.
Cycling it is a bit quieter but because it is an easy ride it is also a popular one.

You don't get all the traffic on the Mosel that you get on the Rhine - the Rhine has trains, highways, barges, cruise boats. I agree, the Mosel is still busy but it is not a major artery on to ports in the Netherlands or a major rail corridor. TBH there are trains down both sides of the Rhine but the right-bank ones are not in the way.

Lavandula

Thank you, this insight is very helpful. We will probably choose the Mosel, stopping at Cochem and a couple other towns to stretch our legs, get a treat, etc. We don't mind driving slower roads. The route then takes us into France, past Strasbourg and back into Germany. Or for another 30 min, we could drive into Luxembourg and then down into France.

We had planned to spend a few days in the Mosel area until our son, whose college graduation we are celebrating and who had said he didn't need to go to Europapark, decided last minute that he did want to go (he works for Disney.) So we had to switch up plans and shoehorn it in at the end of the trip.

normally petrol is cheapest in Luxembourg so at all main border roads you will find massive petrol stations. Just for info

Yes, all the petrol stations are at Wasserbillig. And public transport there is free if you decide to park for a day.

Lavandula