i use both, i clip off the exess then scissor the rest. i know with cockers once you start clipping them you need to keep clipping them as i makes the hair go curly. but i think its a presonal choice, ask you groomer what they think would be best.
I've known about seven cockers (over time) none grew out curly after being done with a clipper, even after years.
Edit: I know some coats can go odd after a clip rarely, like you never clip a show schnauzer or the fur goes 'soft' they pull and tease it out to get the right look. So don't go 100% on what I say lol. But I said what I did because our grooming clients (schnauzers, cockers, shitzu ect) stay strait after many many strips, and 'Lo grows out fine when I let her.