I've been swamped re-acclimating to LAD (life after disney), and I do plan on doing a full trip report, but I wanted to get some max pass info here too.
We were in park mid-March, used MP for entire party (9 the first day, 8 the last 3 days). Loved it and felt it was definitely worth it. We did find some slightly inconsistent behavior with ride breakdowns converting to multi-passes - when this happened, the app would often become nearly unusable for a while as long as the multipass was around, crashing almost everytime we tried to view fast passes. It was a little annoying, but on the flip-side we did have pretty great luck with using rider swap. It took me a couple of days to really get a sense for what attractions were going to go fast and be worth a 90 minute wait, and weather stymied our attempt at a nighttime RSR ride, but by the last day our guest of honor (kiddo who turned 5 this year) was able to go on 10 rides in DCA - before lunch! Plus another 4 in DL even with an extended break for lunch, general looking around, dinner, and Fantasmic! Even on the days where we weren't able to get on as many rides as I would have liked, I still valued the ability to book the FP and get a gauge for waits around the park that I will definitely be booking MP again. Downside - a real lack of photopass photographers in DL. DCA had them all over, but the shots I wanted were almost all in DL, so we didn't get as much value on the photo side as I would have hoped. We also had issues getting some of the ride photos.
So - if you are ONLY getting MP for the photo benefit, it is worth it but just for one person in the party. If you really like going on the FP rides, especially RSR, and you cant or dont want to use the single-rider line, MP is also definitely worth it. I think if I had to choose between MP and park hopper, I would go with MP - but as others have said the biggest value you get is booking them cross park. The only thing that would make them even more valuable is if you could also do the show FP (Fantasmic! and WoC) through the app.