As others have stated, it's all about which commissioning source you're looking into. Pilot selection boards are also extremely dependent on personal situations; look up the current order of merit for selection and you'll get a good idea what we're looking for. I was ROTC, I knew most my order of merit scores before I had to contract (enlist until commissioning -- which comes before rated selections) so I had a somewhat good idea of where I stood in comparison to past year selectees. The bad (and inevitable) factor is that rated selections are entirely based upon FY budget. My year got shafted pretty hard with sequestration and total force recall. For both field training (our officer school equivalent) and rated boards it was about 40-50% selections nationally, it was literally, "if you are in the bottom half of your class (rankings) you are out."
As for OTS you still have the big factor of budget and big Air Force manning algorithms, but you will know before committing to OTS if you have been selected for a rated position. This process is quite lengthy, but OTS in itself is the quickest commissioning route. OTS is also a lot more competitive for rated, they receive far less slots than ROTC and the academy and it is highly subjective to your professional network, civilian flying experience and much higher than average aptitude scores (AFOQT, TBAS, PFA, etc.).
I hope this helps, let me know if you have any other questions.