I just replaced a sulfated year old 14 with a YTX12-BS, I invested in a Battery Tender too since I don't commute by bike as much as I used too. It appears I've made an internet faux pas by not buying another 14, I hate when that happens.
That said I added air to the tires at the same time so I'm sure the pound or two difference will sufficiently reduce rolling resistance to allow my puny 12 to keep a charge.. It also actually fits in the battery box where as the 14 was physically smaller and needed wooden block to hold it in place.
Who'd have thought that a battery thread could be as much fun as an oil thread?