Your two choices are very different.
Moorea is a fairly large island with lots of options and it need not be that expensive. The Blue Pineapple restaurant at Club Bali Hai was very reasonable, as was the snorkel tour we booked through them. We did not stay there but were wishing we had as it looked very nice. There is a bus service you can use to get around, taxis are available, car rentals are expensive but for one day it's nice to be flexible to do what you want. Another option is to rent bikes - lots of riders around - it can be challenging as the island is hilly. We kept costs down by buying fruit, cheese and baguettes for a light lunch. The beaches were nice but not the best we've seen/ there are cultural performances that showcase the dance/ we did self catering so cannot comment on the cuisine. If you want to visit another island I would suggest either Bora Bora or Huahine. Bora Bora has an amazing lagoon - doing a shark viewing trip here would go a long way to getting over your fear - thousands of people have and, as far as I know, not one was attacked! Huahine is what the islands were like before mass tourism - it still retains the old island charm - this was our favorite island and although Moorea and Bora Bora were lovely, they were a bit too touristy for us.
Malolo Island will be a lot smaller and so your options will be fewer. We did not stay on this island but on a couple that would be similar in size. You can avail of a food plan so you will know your costs upfront - there are a couple of resorts on the island so you do have an option of dining out. Getting around will be by foot but with the size of the island this should be easy. Most of your activities will be water related. The beaches in Fiji are nicer in general/ the culture is promoted in dance and kava ceremonies/ the cuisine we enjoyed.
Both islands are safe as is the ocean swimming - the chances of seeing a shark is very small - you really should take advantage of the snorkeling in either place - it is great! One last thing I would like to suggest - check out the forums at tripadvisor.com - Moorea will have lots of comments for, and by, honeymooners and Malolo Island has a great following as well. Another site to check out for Moorea is the forum at tahiti-explorer.com - I found it quite helpful when planning our trip to FP. Would love to hear what choice you make!
