If you are looking for a Kerry for obedience competition, it is better to buy a puppy from conformation or obedience lines?
While I do believe that some dogs are more talented than others when it comes to obedience, I think that it is more important that breeders look at the whole picture when breeding. This means conformation, soundness (both physical and mental), and personality. The breed standard, if properly adhered to, is a pretty good blueprint to work from. Also the same "Hey world, look at me" attitude you would see in a great show dog is the exact same attitude that you would want in an obedience dog. Therefore I would lean towards the so-called "conformation lines."
In many breeds (though not with Kerries, thank goodness!), this belief is carried to an extreme, with "breeders" basing entire pedigrees on obedience titles and little else. Many of them have very little knowledge of conformation, genetics, or other basic principles of good breeding. IMHO this is a mistake, as the resulting offspring (which may or may not become obedience standouts, depending on who trains them) are often little better than random-breeds that bear scant resemblance to their breed standards.
If you are looking for an obedience dog, your best bet is to find a reputable breeder of conformation-quality dogs, insist on health clearances such as OFA and CERF for the parents, select a properly socialized, outgoing, inquisitive puppy, and go from there. While it is always great to see obedience titles (in addition to, not as a replacement for, championship titles) in a pedigree, it is no guarantee that that puppy will be better at obedience than any other properly bred and socialized puppy.
My Kerry, Lav (Casey's Lavish Mischief UDX, 2/3 NA) comes from a long line of top show dogs, none of which happen to have obedience titles. The majority of the other current and recent standouts in obedience (Stellar, Max, Grits, Wheeler, etc.--all of which obtained CDX's or better and have been nationally ranked) come from primarily conformation lines as well.