Most of the automotive press seem to rate the A-Class quite highly, and the 1-Series less so.
The A-Class is at least competitive with the Golf and Focus in most areas (except price, although it is probably a similar monthly payment on a PCP), whereas the 1-Series isn't.
However the lower-powered versions of the A-Class with the torsion-beam rear suspension are not rated as highly as those with the multi-link rear suspension (but the same also applies to the Golf and Focus).
The rear-wheel-drive layout of the current 1-Series is both its biggest advantage and its biggest disadvantage. If handling is more important to you than anything else, and you are buying a version that is powerful enough to take advantage of that, and regularly drive on roads where it makes a difference, that may be enough to sway you, but for many people it makes no sense.