It all depends upon what your collecting interests are and what you use the catalog for.
I have a 2009 Harris US/BNA and a 2011 Postal Service Guide to US Stamps and a Scott Specialized Catalog of US Stamps. I use all three for various purposes.
To start with, the Scott Specialized Catalog of US Stamps (and the Postal Service Guide to US Stamps, which is based on Scott catalog pricing) values most stamps in VF condition; the HE Harris US/BNA catalog values most stamps in only F condition. Furthermore, the HE Harris US/BNA Catalog states in its introduction that they base their values on the following:
Quote:
"The prices quoted in this catalog are the prices for which HE Harris offers stamps for retail sale at the time of publication."
This alone explains why there are significant price differences between the two catalogs and, in most cases, the HE Harris Catalog will show an unduly inflated "value" as compared to a similar listing in the Scott Catalog.
The Scott Specialized Catalog of US Stamps is unquestionably the best resource out there for US stamps and lists many minor varieties that are not listed in the less expensive publications. It also provides various grades for classic era stamps that help to isolate pricing a lot better than just a single figure. Of course, that additional data comes at a price which is reflected in the cost of this more expensive catalog.
The Postal Service Guide to US Stamps uses Scott values, but provides a simplified listing that may be less confusing for the casual collector. Some people also like the fact that they use a format where the stamps are shown on a black background on the left page and all of the catalog listings are shown on the opposite right page, which makes it easy to quickly identify a stamp.
A couple of "advantages" to the HE Harris catalog is that they include BNA. For me, that means an inexpensive way to identify Canadian stamps in my collection. Even though I'm not a Canadian stamp specialist, it provides the basic information for my needs without having to buy a Unitrade Catalog for my minor collecting needs for Canada.
Some do not like the layout of the HE Harris US/BNA catalog since they use a two column format with the stamps and catalog entries shown in rather small size above each listing.
On the other hand, HE Harris is one of the few catalogs that clearly lists First Day Covers in both Singles and Plate Blocks and regular stamps as "mint sheets" that may be useful information for some.
The Scott Catalog has First Day Covers listed in a separate section and Plate Block First Day Cover values are based on a calculated value over their First Day Cover single value listings. Likewise, the Scott catalog does not value sheets of stamps, but one would have to do a valuation based on single, block and/or plate block values and multiply them out to come up with an accurate value for that format.
Also, if you haven't used the HE Harris US/BNA catalog before, don't let the "hard cover" reference confuse you. It is hardcover, but all of the interior pages are contained in a spiral binding within that hard cover.
The Postal Service Guide to US Stamps, which is available for $20 from the USPS or through various bookstores is a simplified version of the Scott Catalog and is quite useful for the beginner collector who is not prepared to purchase a Scott Specialized Catalog. It also serves as a "quick reference" as it is contains only 400 pages as opposed to the 1100+ pages of the Scott Catalog. Unfortunately, if you are interested in postal stationery items (i.e. embossed envelopes and postal cards) the Postal Service Guide to US Stamps is lacking quite a bit of information and doesn't illustrate all designs.
Sometimes it's good to have various catalogs in order to compare information. However, since most collectors rely on Scott Catalog values, that would have to be considered the best source of information. If you don't want (or can't afford) the Scott Specialized Catalog, there are older editions available on the secondary market for much less than the retail value of a new catalog and Scott even offer a smaller version of a Pocket Guide to US Stamps that is also a good reference.
If it were me, I'd opt to buy the $20 Postal Service Guide to US Stamps (which uses Scott catalog values) to start with as it's only $2 more than the HE Harris catalog and, in my opinion, it will provide you with more reliable data.