Interesting decision, given that the Opel is still on sale and the other two have been superseded, but regardless, my money would be going Renault's way. They know hot hatches better than any other company and the Clio is reported to be a much better handler than the other two, which is impressive given how average the non-RS Clio is and how good a chassis the MINI already has.
I also think it looks great with it's flared arches, it's naturally aspirated which I prefer, and I have a soft spot for Renaults anyway so it was always going to be my choice.
The MINI is nice but the non-S Cooper is a nicer looking car and still offers 90% of the fun for much less cost to buy and run, and I hate Opels/Vauxhalls and their typical owners with a passion and the Corsa even more so, so wouldn't touch the OPC with a ten foot pole.