Advocate covers a lot more than frontline. Advocate treats and prevents: heartworm, lungworm, roundworms, whipworms, sarcoptes, demodex, fleas and ear mites. The only things it doesn't cover is tics and tapeworm. Frontline covers fleas and tics.
It depends if tics are a problem for you in your area. I use advocate and Droncit(tapewormer) as mine dont have a problem in the tic department but do scavenge so lungworm is a potential risk.
Hope that helps in someway xxxx