Ht Will and Testament for the Telegraphs comparison of the 'top 20 coolest' Christian and atheist t-shirts. I have to say that the atheist collection shades it, but you can make up your own minds. It's not an objective study 'we have selected 20 of the coolest....', which means the Telegraph possibly spent a few minutes on Google Image search. I'm sure there are better designs out there on both sides.
The only place I've seen Christians wearing Christian t-shirts is at Christian festivals. Where do atheists wear their stuff? Ricky Gervais gigs?
My favourite message t-shirt was produced by the fair trade jewellers Cred, in the days before they specialised: "How you spend controls what happens on the planet." It's full of holes but I refuse to throw it away.