I haven't done either of them, but I'm an experienced caver and they both sound great based on the reviews, and I think you will have a great experience on either. The first decision for you is to decide how adventurous you want to be - tours vary from the very well paved and easy to the tight and wet eg black water rafting.
I've done Spellbound and would highly recommend them, but the Footwhistle tour sounds great too.
Reporting back now. We ended up doing the Spellbound cave tour and it was very nice. Most of the time was spent travelling to the cave but the guide was very informative. There is also a small raft ride inside the main glow worm cave, and photography is allowed.
Thank you Yash G for reporting back on your choice of Glow worm caves tour. I had the same dilemma and you just helped me decide on doing the tour with Spellbound. Btw, I was looking up your reviews but did not see any on Spellbound, as you said it was very nice, I will do the same then.