[mreid]

Both are a pain, but for different reasons. I hate opening a perfectly good intake given you have to drain the coolant, disconnect fuel lines and linkage, remove the distributor (not always), and scrape gasket and sealant. Valve seal are much less invasive, but do require removing rocker arms, finding a way to retain the valves (usually air) while you remove the locks and retainers, and then install rockers and readjust all the valves. Given a choice, I would always go for replacing seals.