When adding some ambience to dry sounds, Do you prefer E.R's or short tails with little or no predelay for the task?

I know for some people is a taste thing, but what is your approach?

Also, does it make sense (for music production) to purchase altiverb just for the realistic early reflections?

Am I missing something from just using Algorithmic E.R's?

I prefer to add what ever makes that track sounds its best in the context of thee mix. you do not do the same thing to everything. What if i want that track to sound like its coming form the back right side of the stereo image?

I do not go into a mix with decisions on what effects i will add and what settings the effects a will be set to until i hear the entire mix.
Agreed it is a taste thing and its also a 'what will make it sound its best thing in the context of the mix'

So my approach is to listen and think about how i want that specific instrument track to sound and ware i want that track sounds coming from. As reverb is one of the tools used to place instrument sin their own stereo image and make a 3D mix.
Every tools has its place. Try the demo, if it has one, and see how you like it. Any effect can make sense, depending on your needs, taste, and your preferences.