Any MNers know Heidelberg or Freiburg well? And airports to travel to/from them.

[MsFogi]

DD2 is going to be staying in both these cities over summer and will be travelling alone with a big (probably v big!) suitcase by air. What would be the best airport to fly into to get to Freiburg (and the best way to get from the airport to the city) and the best airport to fly out of from Heidelberg (and the best way to get from Heidelberg to the airport).
And, last question, what would be the easiest way to get between the two cities?
I had heard about Flixbus but am somewhat scared by the reviews on TrustPilot (coaches not turning up/leaving people at service stations etc!!) so I am now back to thinking train for transfers however I am trying to work out which would have the least transfers/if there are any trains direct from any airports to/from either city.
I'd really appreciate any insight!

Hey op, I live in Germany and have been to both cities for visits. Gorgeous cities, your daughter will have a great time.
Flixbus isn't bad from my experience (I did Tübingen to Munich for years) but I would recommend the train. You can get a direct train journey or one with one change (changing is very normal here in Germany and if the first train is delayed, it's easy to just take the next connection).
www.bahn.de is the website to check trains.
Airports for Freiburg, I'd be inclined to say Stuttgart. For Heidelberg she can fly into Frankfurt or Mannheim :)

Basel Airport is also an option for Freiburg. And the trains are really good from Frankfurt to Heidelberg and Basel to Freiberg so I'd just recommend them

Thanks for the replies so far. One more question - should we book trains or can she just turn up?

I think Basel airport would be easiest for Freiburg, there are lots of buses including Flixbus from the airport directly to Freiburg. Think it's about an hour journey.

From Heidelberg, Frankfurt would be easiest, getting the train direct to the airport. But make sure you find flights from Frankfurt International airport (FRA) not Frankfurt Hahn which is really far away and a PITA to get to. There are no cheap carriers out of FRA any more, but Ryanair flys from Hahn which could catch you out. You'd have to book BA or Lufthansa.
What airport does DD need to return to in the UK?

Alternatively you might get easyJet to/from Stuttgart or Nuremberg, journey to/from Freiburg and Heidelberg would probably be easiest (if not quickest) by Flixbus then.

As PP says, they are both lovely places, I'm sure she'll have an amazing time!

You can just turn up for a train but it's definitely cheaper to book in advance.