Baden-Baden if you're ok with Ryanair...
Basel-Freiburg-Mulhouse if you actually want to enjoy your flight...
It's about an hour from Basel to Europa, there are many routes to take to get there, be it via public transport, which involves trains, or booking a taxi in advance (€100 each way ish) if you're lazy... You could even hire a car, but I don't see the point unless you're going to head off to other nearby parks, but Holiday Park and Tripsdrill aren't great, and you won't get bored of Europa...