personally i wouldn't get either of them. i hate the A5 design and i've heard some pretty bad reviews about the powermax breaking after only two months of use. These reviews were from groomers who used them everyday on multiple dogs so that's something to think about.
i'm a groomer and i prefer andis clippers. they just fit better in my hand. I just bought the new Andis Excel 5 speed clippers at a grooming convention last month and i LOVE them so much. I use them all day long so it was worth the cost.
Now for someone who grooms their own pets at home once every 6-8 weeks something a little simpler would suffice. The Andis Ultra Edge is my spare clipper (used to be my main before the Excel). i bought them 4 years ago to groom Morgan and then started using them daily a year ago when i became a groomer. still good. I also have the round 2 speed andis clippers that i got in grooming school. also good for basic stuff.
as far as blades go, you will definitely need a 10 for sanitary area and a 30 for pads and ears. Any other blades you need will depend on the length you like to keep your yorkie in.
__________________ Kellie  and  Morgan |