a) what do they propose to do?
b) are they competent to do it?
c) should I trust them?
a) I know a lot of Corbyn's general policy positions, and generally approve them. It would be good to have more detail though. Smith (unless I missed it) has not set out many policies, except that he will out-Jeremy Jeremy when it comes to being anti-austerity. Well, they both have plenty of time to fill in the gaps during the campaign - I look forward to that. I have a lot more time for Corbyn's anti-nuclear stance than Smith's support for the current "weapons of mass destruction (for us but not other people)" policy.
b) this is really a two-parter. The first question is, are they competent in an ideal world, and the second, are they competent in the present circumstances?
I think Corbyn's instincts are excellent (on many of the occasions he's run against the political consensus he's been proven right over time), and he's as much of a details man as Cameron ever was, but I don't think he'll ever be a wonk. I'm not sure that's a bad thing if he recognises it and can delegate to trusted colleagues. The question is, are there enough colleagues he can trust, and can he bring himself to do it? More generally, however competent he may be personally, can he make the Parliamentary machine work in an atmosphere where there is talk of splitting the party should he win, or making the leadership challenge an annual event until he loses or gives up?
That question goes wider than the leadership debate - it's a matter of the subversion of the party's constitution by certain members of the PLP, and if that really is the attitude then I would be in favour of deselection, messy though that would be. The PLP can't be allowed to be a dog in a manger to thwart the democratic choice of the party at large (any more, in my opinion, than Parliament should attempt to thwart the democratic choice of the electorate over Brexit, though many people are calling for that, too).
Smith has done a decent job as Shadow Work and Pensions minister, I understand, and obviously he'd have the PLP behind him, at least to begin with. (If they get a taste for the blood of leaders, he shouldn't count on having it long term.) However, he's pretty untested in most policy areas, and has already shown himself gaffe-prone on the few appearances he's made on television, notably by accidentally (I assume) saying he was pro-austerity, and then declaring that he is "normal" because he has a wife and three children - which, however innocently meant, tells you quite a lot about the narrow parameters of his thought, and was particularly stupid when his rival at the time was a lesbian - especially with the recent fall of Andrea Leadsom for similar remarks being in everyone's mind. I honestly can't imagine Corbyn ever saying something like that, and not because he's too canny - he simply doesn't think that way.
c) Here Corbyn scores highly. He has been consistent in his principles for many years, even to the detriment of his career. Smith is again an unknown quantity, but his conniving in the relentlessly ad hominem campaign against Corbyn, and particularly joining in the suggestion (without evidence) that Corbyn was somehow encouraging intimidation, does not incline me to trust him at all. Or rather, he strikes me as neither more nor less trustworthy than most ambitious politicians - that is to say, not very.
So far, in other words, Corbyn is well ahead in the court of my personal opinion. But we have a month to go, so have at it, gentleman! Queensberry rules only, if you please. (Some hope.)