Köln / Cologne / Koeln to Koblenz by train

There are 2 x types of train service between Koln and Koblenz:

(1) These double deck Regio trains, which are slower because they call at more stations, but those upper decks give great views.
They also terminate at Koblenz, so will stand out on the departure screens.

These Regio trains also call at Koblenz-Stadtmitte, which is more convenient for the town center than Koblenz Hbf.

Seats cannot be reserved on the Regio trains, but during the day (before 16:00) it shouldn’t be too difficult to find an upper deck seat(s) from which the scenery can be enjoyed.

(2) Alternative express trains, most of which are IC trains, but some are ICE* trains and yet others are EC trains (Swiss trains with nice big windows)

Discounted tickets CAN be booked online for the express trains; the cheapest of which have a lower price than these Regio trains.

There are 2 x types of train service between Koln and Koblenz:

Other express trains and these double deck Regio trains, which are slower because they call at more stations,

Booking tickets:

Tickets for these Regio trains are not available online, so you can only book at the station immediately before travel.
In contrast, discounted tickets can be booked online for those express trains, the cheapest of which have a lower price than these Regio trains.

So if you’re booking more than a month in advance it’s highly likely that tickets will be cheaper on the express trains.
Some of those express trains can still be cheaper than the Regio trains, if you’re booking only a couple of days ahead.

Seat reservations:

Seats cannot be reserved on these Regio trains, but during the day (before 16:00) it shouldn’t be too difficult to find seats

Though if you want the peace of mind of a reserved seat, seat reservations are available on those alternative express trains.

Final Destination: Multiple destinations including Stuttgart, Nurnberg, Wien and Interlaken

All trains also call at: Bonn Hbf

These express trains are slightly faster than the Regio trains, which also take this route.
And unlike those Regio trains, tickets for these express trains can be booked online.

Though if you will be booking tickets last minute at the station, you can save money by taking those Regio trains.

Book early and save: Yes (on these IC, EC, or ICE trains)

Online usually bookings open: 6 months ahead of the travel date (IC, EC or ICE trains only)

Discounted tickets can be booked online for these express trains - the cheapest of which have a lower price than those Regio trains.

So if you’re booking more than a month in advance it’s highly likely that tickets will be cheaper on these express trains.
Some express trains can still be cheaper than the Regio train if you’re booking only a couple of days ahead.

In contrast to these express trains, tickets for the Regio trains cannot be booked online, they can only be purchased at the station, and they’re not discounted - so you may as well as buy them immediately before jumping on the train.

Once the discounted tickets on the express trains have sold out, the Regio trains become the cheapest option.
So if you will be booking on the day, then the Regio trains will be cheaper.

Reservations:

Book 1st class ticket journey tickets and your seat reservation is included.

2nd class seats can be reserved on these express trains, but it does seem to be extravagant to pay the reservation charges for a journey that takes less than an hour.
However, there may not be any seats available on the most popular express trains, particularly the ICE trains.