Tire Recommendations

My XC70 SE needs 2 rear tires. My front tires have about 10,000~15,000 miles left of life to the tread. My mechanic says I should replace all four tires instead of replacing just 2 at a time since this an AWD vehicle. It's pricey to replace all 4 at one time especially since I want to use only Michelins. What should I do?
Also which Michelins would be best to buy or are there better brands lurking around that I need to know about?
Thanks!

I put Michelin hydroedges on my 2001 xc70 and we love them. BJ

What type of driving do you do? What are the weather conditions where you live? These are the factors that should direct your tire choice. Not simply a brand. And yes you should replace a 4 tires at once. You can keep one of the decent ones as a spare.