Ok, for those saying the VS isn't qualified, what had Shepard done as of being up for consideration? Quit comparing Shepard as of ME2 or even as of the end of ME1 with the VS survivor. Nothing that we saw Shepard do other than having been set up by Saren is relevant to Shepard's appointment. He was already a candidate before we even meet him or get to play him.
Ashley and Kaiden have at least as much experience by the end of ME1 as Shepard did when he was appointed. Futhermore, there are political aspects to Spectre appointments. Garrus was seen as a loose cannon after Shepard 'died', and went rogue. Sure he accomplished a lot, but it was all unsanctioned, and not even under his own name. TIM didn't even know Garrus was Archangel. If he had known, why wouldn't he have told Shepard when Shep was asking about the old crew, esp since TIM had him singled out for recruitment? And once it was known, he went back to working with Shepard, who was considered at least unofficially rogue. Politically that make appointment a lot more difficult. How do people think it would work? Arrest Shep and put Shep on trial while promoting someone working with Shep before the trial is even over?
The VS on the other hand went back to being a loyal alliance lackey, accepting and obeying the transfer order and effectively working the system. We know for a fact they were sent on clandestine assignments and special ops, since TIM claimed not to know for certain what they were up to and Anderson couldn't talk about it with Shepard either. They may well have spent the two years in N7 and/or pre-spectre training for all we know.
That Jack or Miranda might have been better candidates is academic. Neither works for the Alliance nor the Council, so precisely how would either even get considered? Again, why would they put Shepard on trial, and promote a career pirate and mass murderer or an officer from a terrorist organization? (and skip the semantics on definition of terrorist. The Council uses the term, and it is there decision who to appoint).