Yes: firm. The best butters for making laminated pastry are firm for reasons that should be clear at this point: because they won’t melt into the dough as quickly or easily (during rolling and/or in the oven). And that means a flakier, higher-rising finished product.
Certainly, firmness is a factor of temperature. However it’s also a factor of the butter’s fatty acid makeup, and as I wrote yesterday, that’s largely determined by the breed of the cow and the cow’s diet.
Though I can’t afford to buy much French butter, I do know people who insist that butters from Normandy are the best in the world. But in what sense do you mean “best”? If you’re talking about a butter that’s better for spreading, binding sauces and so forth, then Normandy butters probably are among the world’s best. However many pastry chefs in France prefer the butters from Charentes-Poitou because of their firmer texture.
For the day when you feel you’ve truly mastered laminated dough making, you might want to treat yourself to some. Celles sur Belle is a brand of Charentes-Poitou butter that can be found in many specialty shops in the US. It’s probably the most expensive butter I’m aware of (sixteen to twenty bucks a pound), but for the closest possible imitation of fine French pastry, it’s the butter you want.
Failing that, you can asses the relative quality of butters for pastry by giving them a simple squeeze. Standard butters, even when thoroughly chilled, will give a bit under pressure. Try squeezing a tube of Celles sur Belle sometime and you’ll see: it’s hard as a rock when it’s refrigerated. So the next time you’re out hunting for good pastry butter, make like you’re in the produce section and squeeze (just don’t let the grocer see you).