OfficeMax seems to have a better reputation when it comes to honoring rebates. The rebates often come back fast and they offer an online tracking system that you can see when the check has been mailed out.
I only had very limited experience wth Best Buy rebates. They seemed to arrive very slowly though, sometimes after 4-5 months.
Most customers don't want to go through the hassle of sending in the UPC bar code and the receipt. Plus, the rebate checks don't always show up in the mail. Those rebate offers don't attract a big crowd these days. So, a lot of stores will phase out these "rebate" programs.
Terry