Since it seems every other person in the audio world has put their two cents in this thread, why not me?
OP-amps are a class of circuit topology. They can be made from Vacuum tubes (yes, some early ones were), discrete transistors, or transistors on the same die. Every black vinyl disk ever made (analog, and therefore obviously "better sounding"
than a digital CD) passed through an op-amp driving the cutter head.
Discrete transistors (BJT's and FETs) are made using the same processes that are use to make the ones on I.C.'s - they're not necessarily better (or even different)
If you look at "high end" discrete op-amps - like the Jensen ones, they go to great lengths to couple them thermally - makes them work better, by potting them in epoxy. If you want even better thermal coupling, you put them on the same die. Oh wait, that's an I.C.
Anyone who says that Tubes are always better than transistors, or discrete is better than op-amps, needs to first understand that the world isn't that neat - it's not 3 simple classes of devices.
Also, making statements like "but I'm glad that the best ones were made on discrete desks, because I like listening to them better" clearly has no idea what they're talking about - how do you even know what desk something was mixed on?, Was the mastering was done with all discrete circuitry, or were there evil op-amps involved?
An awful lot of energy can be wasted patting yourself on the back about how you like this versus that for some arcane technical difference. If you'd just listen to the music, and take the excess energy you have and put it to some useful purpose (donate the time you'd spend arguing about this or the money you'd otherwise spend on next month's preamp to charity), the world would be a lot better place.