Hi - I’ve been to St. Lucia 7 years in a row (I fell in love with it on my first trip) and have done both. Personally, I prefer the heli ride and I definitely think it’s worth the money (although I was alone and only paying for 1). I always like to get to the resort asap, so I like to that it saves on time. Plus, it’s a great way to see the beauty of the island. The only drawback is that you can only take your carry-on with you, so be sure to pack your beachwear in your carry-on. Your suitcase(s) will arrive by car. On the other hand, the 1.5 hour ride can be interesting for a first-timer (although you can always do that when you depart). Since it’s your honeymoon, I say go for it!!!
I hope that helps. You picked a great location for a honeymoon. Enjoy yourself on my favorite island!