24-105 L v 24-70 L lens?

Hi,

I'm trying to weigh up which lens to get for portrait work.

Clearly the 24-105 mm is significantly cheaper and has image stabilisation.  The 24-70 mm has the advantage of a 2.8 aperture and is lighter in weight.  I'm finding it difficult to decide... any views from people who may have tried both, or even just one?

Thanks

L