The fact that the OT has 8 MIDI tracks, and different length per track, as well as different clock multiplier per track, makes it a clear winner when it comes to sequencing external gear. The LFO designer also rocks hard, and you can actually sequence MIDI synths as well.
Not putting down the A4, I'm in love with it, and think it's a beast. But the OT sequencer is just better implemented.
Oh yes, the micro timing setup in the OT is just brilliant, also.
Overall, you're probably going to end up with both, if you like Elektron's way of working
Cheers !