I’ve never used that addon myself so, as far as an in-depth feature-comparison goes, I couldn’t give you an answer to that.
But with a quick look at AotH, when it comes to the stable interface, it’s mostly about the general layout and structure, and how information is displayed. It looks like with AotH, the goal was to preserve more of the original interface, with the grid-based display of stabled pets, but with the added feature of displaying all stabled pets on the same page instead of split up on several pages.
With iStableMaster, we instead opted for the scroll-frame option to gather all stabled pets into a single frame element for display. Is either option better or worse than the other? I couldn’t tell as this is very much about subjective preferences.
Other than that, you have the display of active pets and how we have chosen to make the interface provide more information from the get-go. We do have plans to include an option for players to be able to choose for themselves if they want to stick with the card-style layout for the active pets, or if they want to go back to showing only the icons. This last part however is not yet implemented, but is planned for a future update.
The feature of “Presets” to allow you to save and quickly swap between entire sets of pets that you can find in iStableMaster, I don’t know if this an option with other similar addons.
The second main feature for iStableMaster, that being “Beast Tamer’s Guide”, and how it intends to provide a gallery for displaying all tameable pets in the game and all info tied to them. This feature is not available for use/testing atm. You have the feature list showing what we want it to include but if you want some form of visual for it, I guess for now, this is roughly what we’re aiming for when it comes to the main interface: https://i.imgur.com/miXpJ1m.png
Again, just a very rough, early sketch.
In many ways, it’s similar to how the collections-interface for equippable items is structured. More is ofc planned other than the actual gallery itself.
But yeah, feel free to compare for yourself with the feature list on the main addon page for iStableMaster: https://www.curseforge.com/wow/addons/istablemaster