They are both owned by Central pet and garden now. Ever since they were purchased the quality of their off the shelf tanks have gone down and the price has stayed the same. Custom tanks are still great, but very pricey because you will pay a mark up through the lfs since you cannot get a tank direct from oceanic.
Quality wise you are looking at the same from AGA or oceanic now, in fact if you look at many of the tanks now, you will see they use the same thickness glass and exact same plastic bracing. The main difference is the styling of the stands and their are several sizes of tanks available from Oceanic that are not available from AGA.