Yaris without a doubt.
I have a 1.5 T-sport Yaris, it is fast but doesn't use that much fuel.
I've had at least 50mpg whilst commuting from home to University, home to the beach, home to a holiday park, etc.
I've had it for just under 2 years (it's an 02 reg) and I haven't had 1 fault with it. It sails through MOTs.
Toyota's (along with Nissan) are known for their top reliability.
As for Renault, it's French, they break down a lot, they come very low down in the reliability 'chart' and they have a horrible feel to them.
Why not test drive both of them and see which one you prefer?
For 4k, you can get a very good Yaris, at least a 53 reg + (they don't need to be brand new to be great). As for a Clio for 4k, you should get a 54 reg, however, you'll spend any remaining cash on repairing it when it all goes wrong!
You can read detailed reviews for both cars on:
www.parkers.co.uk