In some ways they are quite similar. They are both harder to get rid of if you feed them even once.
However I have found the droppings of experts to be usefull at times, but not so for the seagull droppings.
If an expert drops on a seagull they don't even notice. But if a seagull drops on an expert it can be quite amusing, even downright funny
I haven't found a way to add seagulls to my ignore list yet, and some people get upset if you start shooting them.
In most parts
of the world, shooting an expert will get you in more trouble than shooting a seagull.
So I voted for seagulls as being more annoying.