Sorry for yet another what car thread but I have at least narrowed the choice of my next car down to 2!
Both are similar priced (though leon would be about a year older), similar mpg, leon is a bit quicker, astra's ride slightly better are my conclusions from test drives at weekend.
I don't like Astras and would ordinarily plump for the Seat but after having driven a (last gen) Ibiza and a horrifically boring Altea XL, the term "soulless" springs to mind and I think I would say "neither".