S line or Sport with light package..

The brochure is online here if you want to check prices:

http://www.audi.co.uk/content/dam/audi/production/PDF/PriceAndSpecGuides/A3_SB_MY14.pdf

The S-Line does come with Xenon lights, but the Xenon light pack you add to the sport also includes interior light pack and adaptive Xenons (they steer around corners) which both cost extra on S-Line). I think that pack also includes either rain sensor or auto dimming mirror, so the comfort pack is cheaper on a Sport with Xenons than it is on an S-Line.

I've gone Sport with Xenons as that worked out much better for me (plus I didn't want a black headlining). Worth considering that the S-Line might hold more of it's value over 3 years than options would on Sport. I'm planning to keep mine ages, so that dowsnt bother me, but if you're planning to trade in before too long it's worth considering.