Sorry but I can't compare them directly but here's the run down.
We can ignore cells and look at AmpHours for a clue for value and life span. Since most battery packs get about 300 cycles, your battery pack with more AmpHours lasts longer as we don't have as many charge/discharges cycles per year as a smaller battery.
The downside to more AmpHours is weight and cost. But if you plan on 2 more years with the laptop, the bigger battery is what I get.
I have a Toshiba Satellite L755 laptop, and I'm looking at replacement batteries for it. I see Toshiba has a 6 cell one for $130 and a 12 cell one for $150, both of which they say will work with my model. You can view these if you wish here: http://www.toshibadirect.com/td/b2c/findBatteries.jsp .
What are the advantages of the 12 cell? Does the computer run longer with it? Does it have a longer recharge cycle? I would hope the answer would be yes to both, but I've never had to buy a new laptop battery. I've seen cautions about buying batteries from other than the manufacturer, but what about the Micro Center store where I bought the laptop? $130 or $150 seems right expensive.