They are basically the same meds but you only have to take lialda once a day as opposed to 2-3 times for asacol as a maintenance dose. The pills themselves are considerably larger than asacol but it shouldn't make a difference given you have no swallowing difficulty. Other than that, Lialda is the way to go since you don't have to worry about
missing doses as pancakes mentioned.
That didn't stop me though and I flared up as a result of not taking it. Something that simple shouldn't be too difficult but I screwed up. Don't make the same mistake I did and miss any doses!