I use the internally coned ss liners with a screw slot (ampco?) and drill them out to a little under a sixteenth. They last about 3000 shots or two years (maybe less) on my offhand rifle now, but I used to shoot more. The metal in the slot is thin, so they burn out a little oblong and start to self-prime with 3f and accuracy loosens up.
The liners on my chunk guns get replaced at least annually, sometimes I just cut them off and use in offhand rifle. It is easy to tell on a chunk gun when the hole gets bigger, but not worth waiting for it to happen.
I am quite aggressive with the pick, especially on the chunk guns. Dead reliable ignition is worth a little extra money for liners, and it is not that much money or time to replace. I'm sure I'll hear that someone or the other never picks and they have perfect ignition, but pick works for me and is part of routine now!
WL probably last a little longer, but the screw slotted ones are cheaper and easier to replace and work well for me.
On the other hand, I'm with Daryl, the only way not to burn out a touch hole is not to shoot very much! Even the ones I use would probably last some folks 10 years...