Both those engines can give good results, but as I'm in the AGS lair, so to speak, I can only talk for that. I take it you do know about the AGS site, with the game database and the user forum? It's very friendly, and it's easy to get help from the people involved in maintaining and updating the engine. But to be fair, there probably are advantages to using Unity as well, as some people have switched to that after starting with AGS.