definitely go with Harden, he has a lot more upside. While I don't think he will be this year's Mark Prior, i do think he will be better than Radke.
Radke gets drafted because of his name, but in reality he is pretty washed up these days. He'll get a good pounding every now and then. I'd rather have my young pitcher get pounded than an old vet. You can chalk up a young player's poor performance to inexperience, but you will be running out of excuses for Radke.
If Harden doesn't turn out well for you, I'm sure Radke will be a free agent a month and a half into the season.