titanium valves or stainless steel valves for kx250f?

Great brand...I have used them ( stainless) had had very good life, but I did notice a bit of a performance drop.

Paw Paw

Titanium all the way for me. Stainless, especially in a 250f, make the bike feel quite lazy up top.

If you want the Titanium valves to last longer, have CB valve seats installed into the head.

Paw Paw

Xceldyne Ti valves or del west if you got the money.

Copper Boron =$$$$$$

Mow that is a pretty head and ready for action.

Paw Paw

Good power, builder series hot cam. Heavy duty springs, upgraded DLC buckets, vortex ecu, ported tb, moto Tass

The only bike I've ever seen that can possibly benefit from stainless steel valves is an 06-09 CRF 250

I'd stick with the stock part. The materials/coatings on both valve and seat are designed to work together. Mixing up such critical components is never a good idea unless the stock part has reliability issues. Many aftermarket valves, even very high end ones, are made using whatever front, blackface, backcut, stem and seat shapes their production line uses and isn't optimized to your particular engine like the stock part. Why risk it?

Well when replacing valves you either need to replace your seats or have them recut so it really shouldn't matter about stock materials etc. he'd have the valve seats cut to the valves he's installing.