I can't speak for @shazzbaa, but there's a definite difference between individual cons!
I've tabled at 3 different cons - several times at one of them, over the course of several years of it being organised - and what sells, and how well, varies depending on the con.
I sold most of my books/fanzines at Stockholm's International Comics Festival, which is explicitly geared towards small press publications and self-published comics - the crowd who comes do so looking for comics.
The other two cons, I sold more prints/gadgets, since they were 1.) an anime/manga fandom con (and I don't sell fanworks), and 2.) a fusion of a gaming con and a comic con, where most of the crowd came there looking for game-stuff.
So if you're looking to sell comics, I'd say go for a con that is geared towards that, instead of just having a tiny Artist Alley in the middle of a sea of professional publishers/companies.