Good question -- but all filters are not created equal. Some are disposable and others are cleanable. Pleated disposable filters last longer (maybe 3 months) than the cheapest of the fibreglass filters (one month). In fact the 3M Filtrete filter, the top of the 3M series of filters, is rated as one of the best because it is both pleated (more filtration area in the same size filter) and has an effective electrostatic action to help trap fine particles.
Warranties will be found on some of the re-useable cleanable filters because they are supposed to last for a long time. There are several cleanable filters that claim passive electrostatic properties, like with the Filtrete disposable filter. They are very expensive and claim great filtering action for years, but independent research by CMHC has found that these loose their electrostatic properties after a few cleanings. Active electrostatic properties can be created by having actual electric wires included in the filter, like a miniature version of a 4 inch electronic filter. Remember that although more efficient that many other 1 inch filters, they cannot deliver the same job as a 4 inch electronic filter will give. All electronic filters must be kept shinny clean for good filtration.
For an unbiased look at filters check out the CMHC site for the About Your House pamphlet called Your Furnace Filters.