Upload & Sell: Off
Animoto is great and will pay for itself if you produce a lot of them each year, if you sell them as a value-add. They do tend to sell themselves, so long as you've listed them as an option from the beginning. PM me for an animoto promo code if you'd like one.
I've been using them for several years. My approach is to use Audacity to splice together three tunes and upload that file, with a target length of 6-8 minutes and about 90-130 images.
The drawback to Animoto is you can't always control exactly when certain images hit certain parts in the music, although the better you understand the engine, the more control you'll have. Standalone programs give you more detail-level control, but they also lack Animoto's sophisticated transition and motion effects. The standalone programs do have those effects, but I find Animoto's balance to be excellent. If I tried to add animations that way, my slideshow would likely just look horrible, but Animoto tends to add energy and interest without being too distracting.