Both Ivomectin (in its various tradenames) and Panacur only kill the worms that are present, neither are a preventative.
From memory the Panacur for sheep is a different strength, so you would need a pig one, and as others have said only does internal worms, not external mites/lice, although you should easily be able to see if you have external problems, so if using the pellets is easier then go for that - if you only have a few pigs it is fairly simple to poke a portion in something squashy eg pear and hand to the pig.
Only problem is that Panacur is I believe being withdrawn form sale due to lack of sales and high cost of Gov. licencing making it not worth well. Not definate on that one, but someone told me I remember, though quite who I cannot remember - oh to be young again!