I don't have actual advice, just a "shared experience". We've used a CPA for the last 3 years. Every year I still throw my numbers in to Turbo Tax to see what the difference is, and every year he saves us more money than Turbo. This year, it went opposite, and the numbers looked better on Turbo by $1500...
I stopped comparing them, because it was driving me nuts always having different numbers. I'm going with the "he's a well respected CPA in the area, I need to just trust him" mindset.
That being said, you can have another H&R Block person look at last years return, and they can get you money if in fact the last guy made an error. A friend of mine did that a couple years ago.
And, i'm not saying I wouldn't necessarily distrust H&R Block or not, but maybe look into getting a dedicated CPA? I ask mine questions all year long, and only pay him at tax time... It's nice to have someone I can bounce tax questions off of all year long.