Here is what I worked out to make the decision. It may seem a little complicated, but it's just a matter of answering yes or no to the situations. This does not take into account any discounts obtained from the AP, such as merchandise, room discounts or TIW. This is based on prices from Disney, not discount brokers (which actually doesn't really affect the decision).
MYW = Magic Your Way ticket
PH = Park Hopper add on
WFM = Water Park Fun and more
NE = Non-Expiring
AP = Annual Pass
PAP = Premium Annual Pass
WPSA = Water Park Single Admission
For One Trip of 14 Days or Less
If you will visit the major parks 10 days or less, buy a 10d MYW PH - $306
If you will visit the major parks 11 days, buy a 10d MYW PH and 1d MYW non-PH - $386
If you buy a MYW as above, and will visit the water parks only once - buy a WPSA - $43
If you buy a MYW as above, and will visit the water parks more than once - add WFM to the MYW ticket - $54 (watch the 14 day expiry)
If you will visit the major parks 12 or more days, buy a
DVC-discounted AP - $391
If you have an AP, and will visit the water parks 2 times (or less) - buy WPSA - $78 (with AP discount)
If you have an AP, and will visit the water parks 3 or more times - buy a PAP - $504 ($113 more than AP)
For Multiple Trips Within a Year
If you will visit the major parks a TOTAL of 6 days or less, buy a 6d MYW PH
NE - $378 (with a discount broker this increases to 7 days)
If you buy a MYW as above, and will visit the water parks only once - buy a WPSA - $43
If you buy a MYW as above, and will visit the water parks more than once - add WFM to the MYW ticket - $54
If you will visit the major parks 7 or more days, buy an AP - $391
If you have an AP, and will visit the water parks 2 times (or less) - buy WPSA - $78 (with AP discount)
If you have an AP, and will visit the water parks 3 or more times - buy a PAP - $504 ($113 more than AP)
A Word About Non-Expiring Tickets
Non-expiring MYW tickets can have great value if your trips do not occur within the same year. Since this thread is more about an AP, I haven't done a lot of analysis other than the following observation.
NE MYW have value only if they completely cover your needs for entire trips. For example, if you have a 10day NE and 6 days are used, you get the value for a trip where you only go to the parks 4 days. If your next trip is going to be longer than 4 days, save the ticket and buy an expiring ticket for this trip.
There is also a sweet spot for people who do the water parks. A 10day Non-Expiring ticket costs $213 more than the expiring version. This non-expiry applies to the water park options as well. Even if you use all 10 days of your major parks in a single trip, the water park admissions are still left. This means that you paid $267 for 10 water park admissions ($54 for the WFM option and $213 for the NE). This works out to less than $27 per admission compared to the gate price of $43. Or it could mean not having to pay for the WFM for several trips. This is a good option to consider if you go 1 or 2 times to the water parks on each trip. If you do the water parks 2 times each trip, 5 trips will cost $270 in WFM options compared to the $267 doing it the NE way (a breakeven proposition until you consider the inevitable price increases). If you do the water parks once each trip, the savings are as much as $160.
Anyway, that's my analysis on a DVC-discounted AP versus MYW decision.