Hi Nicholas,
I would strike straight away with a sprat, although I tend to go for something bigger for wobbling. Sardines are a bit soft, but 15-20cm herrings are excellent for wobbling, or a similar sized roach or dace where allowed. With baits of this size you can sometimes entice a reluctant pike to have a go when smaller baits don't seem to do it. Some people like to mount the fish with a bent body, so that it spins and twists, but I prefer to mount it straight, with a big single through the head and a treble half way down the flank. This way you can impart whatever type of movement you want with the rod tip.
Also, if you get a follower that refuses to take, it is sometimes worth letting the bait sit on the bottom for a few minutes, as this can tempt them to pick it up.
Hope that's useful.