I've just joined BA from the low-cost world. I was quite disappointed in both the level of the pensionable pay (only 35k) and the level of contribution (17% overall), but it didn't stop me signing up.
My previous pension scheme was woeful by comparison (13% overall) although the pensionable pay was full basic salary.
Overall I calculated I will be better off due to the tax position after allowances, increase in basic salary on an annual basis, and therefore higher annual contributions on an ongoing basis, and the option / ability to increase my personal contributions over my career.
Besides that - it's BA. Who knows what could lie round the corner?