You know, I've been asking myself that question lots & lots lately....
What time of year to go???
However, what I've learned as a repeat visitor, any time of year is good for ME.
I can walk around all four parks and find every attraction without a map. I know the shortcuts through stores and hidden little pathways to avoid the crowds.
If there is something new I want to see without waiting in a long line, I make sure I'm there to see it at rope drop.
I don't worry about seeing "everything" each trip.
We successfully took a pair of friends that had never been to WDW before during Easter week and they were perfectly happy to follow where I led and we saw an incredible amount of attractions in 4 days.
So, I guess my recommendation for April is if you have an experienced person in the group and the rest of the group is willing to follow, then yes, April is a great time to go.
If not, April is still a great time to go, but the group will have to lower its expectations as far as how much you'll be able to see. However, quality is often far more important than quantity.
Do your research, read about the attractions and decide what you really want to see. Make those a "must do" first thing each morning, then the rest will be gravy!!
Carol