In reply to Catriona:
+1 for the point about rope length, unless you know 30m is enough for your local wall, and you're only going to use that one wall. 35m minimum for a rope if you intend climbing at various different walls; even that won't be enough for the longest routes at some walls.
Regarding those two ropes: the Beal is thicker than the Mammut - you'll probably get a bit more wear out of it, and it'll probably feel nice and comfy in the belay hand, but be aware that it might be a bit thick for some belay devices (e.g. Grigri 2).