According to Consumers Reports November 2011 test of over 60 car batteries you shouldn't just buy just by brand. Performance varies by size and model as indicated by their rather comprehensive tests.
"Many DieHard and Everstart batteries are recommended, for example, but others from those brnds scored no better than midpack in our tecting. Moreover, Bosch, Duralast, Kirkland Signature, and NAPA models also performed well in certain categories."
DieHard models are top rated in four of the six groups Consumers tested. Group 65, 34/78 & 78 Group 75, and Group 48.
In Group 24, the Interstate Mega-Tron Plus MTP-24 was ranked first with Diehard Gold ranked second. Bosch was top rated in Group 35 with the Everstart Maxx 35N ranked second.
They noted that the much improved Diehard ratings resulted from improved specs and a switch of suppliers.
Three performance factors were cited as the most important in choosing a battery: battery life, reserve capacity nd cold cranking amps (CCA).
Also interesting to note is that the Diehard has the best warranty ( 36/100 ) and WalMart's Everstart the worst...just 36 month replacement with NO pro rated coverage.
CR also commented on the fact that all battery prices have risen after staying stable for many years.
Bottom line is...choose the correct size battery for your use, your driving habits and always get the freshest battery possibe by checking the shippng codes on the battery case.
Their overall recommendations:
For cold climates:
Diehard Gold 50678 $110
Kirkland Signature 12866 $75
Interstate Mega-tron Plus MTP-24 $120
Diehard Gold 50624 North $105
Duralast Gold 24-DLG $90
Kirkland Signature 12865 $60
Plus Start 50235 $70
Bosch Premium Power 75-730B $80
Everstart Maxx 75N $80
For Temperate Climates:
NAPA 8465 $85
DieHard Gold 50534 ( South) $110
EverStart Maxx 34S (South) $90
EverStart Maxx 78S (South) $90
DieHard Gold 50523 (South) $105
EverStart Maxx 24S (South) $80
Everstart Maxx 35S (South) $90
DieHard Gold 50535 (South) $110
DieHard Gold 50575 (South) $110