Mainz Hotel Recommendation - NOT near train station

Can you give me recommendations for a nice place in a picturesque area, Old Town perhaps?

You are correct that the station area isn't picturesque. The reason I and others are content with the station area is largely one of selection and convenience. And it's just a few blocks from those hotels to the pedestrianized commercial zone, where things quiet down, traffic ends, and shops/restaurants line the paths toward the Marktplatz and the old town.

There's not much right in the old town, but I'd look into the Hof Ehrenfels for the atmosphere and location you seek. Haven't stayed there myself.

I usually stay at the Ibis, about 3 blocks up Augustinerstrasse to the south from the southern end of the old town zone. I like the location a little better as it's closer than the main station area to the Rhine, the city park, and Mainz's core sights and old town - and because it's 1 block from a secondary station (Mainz Roemisches Theater) where a Roman Theatre was unearthed a couple decades ago. The immediate area around the Ibis is more city than old-town though.

Can't advise you on parking. Never had the desire to drive inside Mainz when I was renting in Europe, and in recent years I became a 100%-by-train traveler.

If you have a car why Mainz and not beautiful old town Eltville, Schloss Reinhartshausen or very special tip Eberbach Monastery? All just across river Rhine.

Mainz is an ok city but I fail to see the attraction. There are nice restaurants, cathedrals and good shopping. (I lived 20 minutes from Mainz for more than a decade) But it’s no place to go out of your way for.

Kloster Eberbach as mentioned by another poster here is fantastic. Wine, food, a monastery and lodging all combine to a delightful destination.

The trouble is, most hotels in Mainz are near the train station. One exception is the Hilton but that one gives a strong conference hotel vibe (I went to a conference in the adjoining hall last year), and Hof Ehrenfels as mentioned.
I really enjoyed my stay at Hotel Hammer last year, but it is right in front of the station.

What you want is the Hyatt Regency. It's on the edge of the old town, on the banks of the Rhine with a great view up and down the river, a very good restaurant, and it is built into the old Fort Malakoff.

We have stayed at the Ibis on Russ's advice and had a good stay. It is an easy walk to downtown.

I would choose the Hyatt, near the Römisches Theater stop. (do go exploring here, as well as the near-by St. Stephens with the Chagall windows)