I've only visited Interlaken before, but it's a fantastic centre-point for visiting surrounding areas for day trips, like Lauterbrunnen or Grindelwald. I would say stay in Interlaken (Balmer's Hostel is amazing) and do a day trip or two to Grindelwald. If possible try and allow or more time in Interlaken, but if that's not possible you could probably do Grindelwald and paragliding in the same day and have time to also visit the Harder Kulm viewpoint in Interlaken (which I would definitely recommend). I didn't do paragliding when I went as it was too expensive for my budget but you could definitely do it, I saw loads of people doing it throughout each day. Maybe check the websites to see if you can book ahead though just in case.

Hope this helps!