Tecumseh appears to be in financial difficulty.
I'd be a bit leery about future parts support??

I don't think you can go wrong with either engine, however, ariens in my eyes makes the best snow blowers. I have tecumseh on my ariens 824 classic deluxe and it starts first or second pull and runs strong. I also have a briggs 10hp briggs intek on my mckissic 12pt10 chipper and it starts and runs just as well. I'd focus more on the quality of the machine in whole vs just the engine. As long as you perform regular maintainence and don't use stale gas, each will run fine.