well, i own both… i would say it depends on how you write music:
if you like to PLAY i would choose MPC. if you like control in programming i would recommend OT. Both are good in their way to control midi gear.
pro OT: if you sequence a lot… the sequencer is 1000 better than the MPC, i you want control over parameters. if you think of more dance/electronic styles the sequencer always results in nice unexpected patterns. the crossfader is absolut amazing… switching several parameters of several channels at once is s super easy to customize… matchmaker.
contra OT: its a lot of work and clicking to load all the stuff for a liveset into the OT… once its there and setup the way you want, OT is fun though
pro MPC: never experienced a faster workflow in chopping, trimming and assigning samples to pads… the pads are amazing and feel gorgeous. also the midi-setup (with MPC as master) is amazing fast: setup channel and go! for controlling midi gear i prefer the MPC over OT (you also can have extremly long sequences)
contra MPC: the sequencer is good for PLAYING stuff into it… programming it is a waste of time (and at the moment you can only program note, volume and pan). when using the audiotracks/clips at the moment the system sometimes does strange things, sometimes crashes… would use it that way in front of a audience at the moment…
My setup: MPC is controlling 5 synths and the AR and OT, all routed to RME with ADAT-expansion for parallel live recording into cubase (synced)… the OT does more of that strange stuff to just one or two samples, the MPC does basic sampledrums (supported by the fat sound of AR)… on top the MPC does some keygroups sampled from my analog devices (synthsstrings, basses)… all other gear just receives midinotes so i can tweak the knobs like hell live.
in addition: i somehow prefer the OT effects over MPC… dont know why, but the filters feel better in OT… MPC effects are only good as “background filler”. Mostly i just use the delays and flanger. but thats my personal opinion