Frankfurt Train Stations

For me, it would depend on:

1) What time does your flight arrive?

2) Where are you going?

3) What time is your train?

When I visited Frankfurt in the 1980's the area around the main train station was well known for being an unsavory area, with houses of prostitution. I would not recommend staying in that area. The airport station should be fine.

Your final destination matters a lot.

After a long flight, I usually I have a little steam left in me for a short train ride, and making a little progress in the right direction makes sense to me. If you're heading in the general direction of MUNICH, as some choose to do from FRA, FRANKFURT itself might make sense as it's only a few minutes and on your route. Also on your route and 90 minutes from FRA by direct train is WÜRZBURG, a smaller city with much to offer.

Other final destinations taking you in other directions might call for a stay in MAINZ, (25 minutes by direct local train.) It's my favorite stopover near FRA. COLOGNE is only an hour or so from FRA if you are heading to certain destinations in northern Germany.

We spend the night in the city: twice near the Hauptbahnhof and once on the edge of the alte stadt, which we liked the best. The area near the station is not an unseemly as it once was. Within a short walk there are several nicer hotels and the old center is only a short U-Bahn ride.

If the purpose of staying a night is to hedge against delays enroute, then it probably
doesn't matter too much. There are plenty of decent hotels within a few blocks of
the Hauptbahnhof, and the area, while a bit gritty, is just fine during daytime and
early-mid evening hours.

But there are plenty of hotels around the airport as well if you are getting in late
and just want to hit the hay. Along with the Sheraton and Hiltons within walking
distance, there are a lot of more reasonably priced (chain) hotels within easy walking
distance from the Gateway Gardens S-Bahn stop, one stop from the airport terminal.

As noted, without any more criteria from OP, it's hard to provide any more advise.

I usually opt to continue on to my final destination since the day is pretty jetlagged and all. It depends, of course, on your arrival time and the length of the train ride.

If your incoming flight arrives in the AM, your hotel might not let you check-in anyway, so you might as keep moving.

To a large extent it matters more where you are traveling to. An opinion from 40 years ago is worthless; even one from 10 years ago is outdated. The fact is there are very good hotels you can reach right from the terminal at FRA, but you may have better options.

If I was traveling outside of the immediate area I'd look at a place on the train line in that direction. For example, if I was going anywhere that's past Mainz, I'd get a hotel in Mainz. The same with Hanau, or Darmstadt, or Bad Homburg. I'd do this because there's a better chance of finding a nice hotel at a reasonable price, because you're not right by the airport, and don't have to stay right by a train station, and because those are nice towns to visit on their own.

Thanks KGC, the sort of insight or 2nd opinion that I was looking for.

I too question any kind of recommendations from a visit done 40 years ago. It would be like me making recommendations for Col. Ohio which I left almost 40 years ago. When I visit, I barely recognize my home town anymore.

For Frankfurt, though there are decent hotels near the main station, like Hamburger Hof, Flemings, Cristall, Hotel Nizza, Hotel Victoria, I think I would go 2 stops further with the S-bahn (S-8 or S-9) from the airport to the Hauptwache. Lots of nice hotels around here and easy access to some sight seeing, which might be nice after a trans-atlantic flight.
Try Motel One Römer, the Moxy, Flemings City Center, the Hilton or Steigenberger Frankfurter Hof.

Where are you going next and do you have any specific interests?

I agree with the Steigenberg or the Hilton, and both the Marriott and Sheraton right at the terminal are nice (and soundproof).