Hello Barb,
Excellent choice for for your fortieth and congratulations.
Both are absolutely beautiful but somewhat different.
Wahweap tends to have more services I think, Bullfrog is quite remote and limited. Also Page with all it's services and convenient shopping is available from Wahweap too. In Page you can easily wait to do your shopping for the trip, with Safeway and Walmart being there. Bullfrog only has snack food available other than the restaurant at Defiance house, so you will need to bring everything with you and if something important is left behind, you will likely have to go without it.
If you are okay with camping in the openness of Bullfrog bay or the Wahweap bay area, ( both are somewhat exposed to wind and constant wave action) then either is an okay choice that way. It is preferred by most to get away to a private and calmer spot. This to me is one of the biggest differences in the two: at Wahweap it is not as far to find a nicer spot. Leaving the Bullfrog area it is two hours going south to find any camping ( Iceberg/ Slickrock canyons area), and similar heading north.
Do not short yourself on time. If it is within your budget and time constraints, I would recommend even longer than 5 days. 3 days will go by like no time at all and will only leave you all wishing for more time. ( Some of us have trouble leaving after two weeks there. ) Considering that one day on each end of the trip will be spent largely on acquiring and familiarizing you and your crew with the boat, arranging gear/food etc. and then getting to a good camp spot and then getting back, turning in the boat etc. 3 days would really only leave one free day to enjoy. Although I have always enjoyed the time chugging along on the way to a camp also.
Be sure to tie the boat to the shore like your life depends on it. Storms can come up quickly and a loose boat in a storm can be very scary and dangerous. If you are secured to the beach properly, a storm is no big deal. Just batten down and let it pass. Please be aware that as Beautiful as Lake Powell is, it can be hazardous if not treated with due respect.
I hope I haven't left you feeling intimidated, it is totally doable and will be a treasured time for you all!!
In closing you need to be aware of the following; WARNING; Lake Powell is absolutely addicting!
Hope this is helpful, I'm sure others will help with good advise too. You have the time of your lives!!
Fish Finder.