Train travel in Germany: Should we be buying tickets weeks early or day of travel?

For your travel dates you should be booking long-distance train rides like these two tickets NOW for the best prices.

The best prices are called "saver fares" (Sparpreise) - they are generally non-refundable, so book them ACCURATELY - take your time with the DB site. Prices go up as tickets sell. Prices vary depending on demand at any given time - a 6 am departure is more likely cheaper than a 9 am departure since very few people want to get up at 5 am to catch a 6 am train.

You must ride exactly as scheduled with saver fare tickets. These tickets are sold for journeys using the high-speed long-distance trains (ICE, EC for example.) So be prepared to do what you need to to in order to board your train on time.

Long journeys often mean changes of train. Some journeys require more changes than others to a given destination - so go with fewer changes whenever you can, not just for conveniences, but also because train A might be late and not arrive in time for train B's departure... the more changes you have, the greater the chance that you'll get stranded somewhere for an hour or longer. This result has become somewhat common in recent years as the ICE etc. trains have an earned reputation for being late.

Reservations are separate procedure from ticketing. If you want reservations (a good idea usually) get them soon as well.

Additional guidance: https://www.seat61.com/train-travel-in-germany.htm

Highly recommend you fly Berlin to Basel. That's a very long train ride. Easyjet tickets are @ $60. Flight time 1.5 hours.

to emphasise Russ's point about accuracy, if at this late date you don't actually know who will be travelling
"6 to 8 of us will be travelling together in Germany"
it would not be wise to buy too few or too many nonrefundable, non changeable tickets.

You may want to wait until you really know. Same theory as buying 6 to 8 airline tickets

and yes, Berlin to Basel is some train ride.

Regarding Train versus Plane.
Plane will be around 5-6 hours all in downtown to downtown.
The train is 7h15.

I would take the train. More options during the day, and you do not need physiotherapy afterwards.

Tip: When booked in advance 1st class is often not that much more expensive than 2nd class. I always go 1st class in Germany. You get service at your place, and 2nd class is often very crowded.

Pay attention to reservations: They are not automatically included, but I would reserve seats anyway.

The flight is 2 hours on the front end and 1.25 hours on the back end plus flight time so, 4.75 and I could believe 5 hours. The train is 45 minutes on the front end and 30 minutes on the back end plus 7.25 hours on the train so 8.5 hours total. So your choice seems to be 5 hours with a flight or 8.5 hours with a train. I suspect that the flight has better on-time performance than the train based on the posts here about DB long haul trains. But it isn’t that easy. That EasyJet flight may only go one or two days a week depending on the OP's travel dates. The train will cost you maybe $150 which is the minimum the flight will cost you if you throw in a checked bag.

Tough decision. As for when to buy the train tickets. Find your train on the DB site for a date next week. See the price. Now look up the same train 3 weeks from now. Same price? You can wait. More expensive next week? Maybe dont wait.

I editied this to fix a few errors. But the result is the same.

Thanks so much everyone for all of the good ideas that you have shared with me. I really appreciate each of you taking the time to offer information to help us with our trip.
John

"The train is 30 minutes on the front end and 30 minutes on the back end plus 8 hours on the train "

It is 7h15 on the train, and 5 minutes at the front and 1 at the end... You do not need to be half an hour in advance at the station. And the moment you step of the train you have arrived.

And don't forget to consider the time needed to get from down town Berlin to the airport, and afterwards from Basel airport to downtown.

So the choice is between a 7:15 one seat train ride, where you even can pick from several stations in Berlin, versus a train ride out to the airport, followed by 2 hours of queuing, standing around and basically not being able to relax because. Followed by 1 1/2 hours of torture on a plane, followed. by more waiting, and then a bus ride in to Basel. And that all to save a few hours.

(They should make sure that two normal sized males are never sat next to each other on a plane. That just does not work...)

From what I can see, the Berlin-Basel flight is 1-2x per day, either in the early morning or the evening, meaning that you can get most of the day either in Berlin or in Basel, instead of spending ~8 hours (with the usual DB buffer) on the train.
If you'd rather take the train, e.g. for environmental reasons, for seat comfort, or for fear of flying, it's doable, but the flight will save about 3 hours.

balso,

I looked April 20 to May 20 based on the OPs late April, early May description. Only 2 days a week with flights.

Balso, i agree on the train vs plane. When people complain that you have to add hours of time to the flight time for the longer drive to the airport and the required early check in time. Thats fair. I added 3.5 hours. But then they treat the train like it stops at the hotel room door and assume when someone is riding a train for the third time in their life from a station they have never been to in a country where they dont speak the language that they will show up 5 minutes before thr train leaves. Life doesnt work that way; at least not my life so i add an hour to the schedule time.

I would certainly buy a ticket for the long distance trains early, but maybe hold off a bit on the seat reservation. My reasoning is that about a 1/3 or more, of the routes I bought, had changes that cancelled the ticket. Sounds ominous, but that is like winning the rail lottery, it means you can hop any train on that route that day, however, you lose your seat reservation, and have to go through the process of getting a refund and making another. So I usually buy my ticket, then closer to the travel date, make the seat reservation.

Of course, if you want 8 people to sit together and want the facing each other seats with a table, then maybe the seat reservation makes sense, those seats go quicker, just potentially more work if the schedule changes.

I looked April 20 to May 20 based on the OPs late April, early May description. Only 2 days a week with flights

Ah, I see, I looked right now, and there must be more flights being winter/ski season.

I was sort of shocked. Lots of flights before that 3 week window and a lot of flights aftter. This all depend on the OP's dates. I hate guessing. Its an example of why this: https://community.ricksteves.com/travel-forum/general-europe/what-should-i-do-with-4-days-in-budapest-or-london-or-rome-or