We've been using the 1500 for a little over a year now. It works better than any other filter we've tried, but it is a bit pricey for us as there seems to be a drastic reduction in filtering after 30 days.
We have year round allergies, and one indoor, short haired cat. We replace our filters on the first of every month. We have come to dread months with 31 days, since without fail, all 4 of us start sneezing after the 30th day. It's like flipping a switch. The cheapest we have found the filters is at our local hardware store, which is cheaper than anywhere else, online or otherwise. There doesn't seem to be a price break on the 3 or 6 packs that we have found, so we buy them one at a time, but like I said above, it can be pricey at $20/month.
Regardless, if we want any relief at all, we use Filtrete Ultra Allergen Reduction 1500.