Abhoth
16
I use my OT as a kind of hardware DAW. Basically it replaced a PC with Cubase. So to me the OT is the most important piece of my setup. The A4 is more ‘specialized’ imo, doing a specific task very well. So where to start is probably very much a question of what you want to do. I personally think the OT is incredibly fun and the logical device to start with. I’m actually a bit surprised to be in the minority here, even if we are in the A4 section of the forum. I don’t think you can go terribly wrong either way, though. You’re in for a ton of fun whatever device you go for. 
I don’t think it is easy to ‘transition’ to the OT from other gear, though. It is a unique device that require patience to get the hang of. I don’t agree with those claiming it is complicated, it is just … different. The A4 is simpler in this respect. Particularly if you already know your way around synths in general. I don’t know the AR.