No contest, spray. Once you've used a spray you'll never go back, on
anything more than 2 or 3 panels. But you need to use something designed
for
the task otherwise the nozzle will likely clog.

Agreed on both points. I bought one few years back for about £50 from
Machine Mart. A breeze using spirit based preservative but absolutely
useless with waterbased stains or the emulsion that the instructions claimed
it could cope with. I know the price has dropped for these things perhaps
the quality has increased as well.

Sam