Which one has fewer failures and headaches? I would imagine the slip x slip type? But not positive so I came here to seek some advice. Thanks!

Personal preference. Neither will fail if you install it correctly.

A lot of people prefer threaded because they can be re-used.

Ahh good to note - I would've thought that both could be reused. Thanks!

TxT, I have helped too many friends cut their glued slip style apart when they decided to move or replumb. Yes you can use unions but it always seems to stick out too far to slide off the stand, the wrong half of the union was glued on or you cannot find the same brand and style of union at a later date so you end up with half a union.
I prefer to use TxT along with plenty of unions for greater flexibility. I have done a sticky post on many of the reefing forums on correct bulkhead installation, not sure if its on NR or not?

+1

after having to fool around with too many arsed up glued bulkheads that have had to be replaced i've made it a point to always use TxT or at least threaded on the dry side of the bulkhead. For stand pipes and such it doesnt need to be threaded on the wet side, slip works just fine..

Thank you all for the dissemination of information!

+1

Just go with threaded. They will both work equally well, but threaded is easier to remove if you ever need to.