Modern Stamp Catalog Values

Which catalog in your opinion provide the most accurate reflection of stamp value for modern stamps, particularly 1990's to present? Brookman, Scott, Mystic, Gitner's buy list, or ebay sold listings? I realize the vast majority of modern day issues aren't "investments" but are there some 1990's to present series or issues you would pay over face value for and that might command a consistently significant over face value premium in the future in case one loses interest in the subject matter of the stamp and needs to sell?

It really depends upon how you are buying or selling the stamp in question.

If you pay face value for a 25 cent stamp by mail order, it costs 25 + 66 cents for a total of 91 cents but its value is not 91 cents, but less. All the listed catalogs and price lists are for one stamp and changes if you are ordering larger quantities such as a full sheet.

Normal minimum Scott value for a mint stamp is 2 times face.So if you are looking for stamps with a premium you need to begin looking for stamps whose mint values are more than double face.

Now those same stamps being sold to a dealer will be purchased for LESS than what the list price is and even for less than face value AND they will NOT reimburse you for the related expenses to deliver the stamp into their hands, be it postage, gas, bus fare, Uber or Lyft expenses and the like.

Edited to add "er" to make deal dealer. And to say you best investment in modern stamps are the forever stamps which will continue to rise in face value even after you purchase them. And you need to understand that often the best way to recoup highest value is to use mint stamps as postage at the rate of full face value.

IMO standard catalog values for modern issues are like a solution to a problem that doesn't exist. Pretty much any modern US stamp with a substantial premium value falls within the EFO category. If a 29-cent face value stamp fetches 2 dollars on ebay, do you really need a catalog to look to for validation?

Forever stamps

There is the catalog value, and there is the resale value. 33 cent sheets are a little easier to sell right now than 34 cent sheets because two 33 centers make up a 66 cent first class rate.

Love and flower stamps in usable denominations are often in demand for wedding planners mailing invitations.

Some celebrities and other topicals can receive a higher premium, but which ones are popular changes with the wind, you can't predict what will be popular tomorrow or 5-10 years from now.

Conversely, I think I remember seeing the 18¢ Alcoholism and 10¢ Retarded Children on Gitner's Buy List, possibly sheets that are /unpopular/ and maybe often missing from many collections.

I agree with the others, Forever stamps are the best "investment" certain to go up in value. At least until they are all demonetized when the USPS goes digital like the UK.

There are some that are not EFO as well. depending on one's exact definition of "modern".

Not all UK stamps have been invalidated. Only the permanent stamps have been invalidated. Christmas stamps that also saw the data matrix added remain valid without the data matrix. Adding of the matrix code does not mark 'digitalisation' as that is an ungoing process. It is an added security feature that has a digital element.
Parts of the mail processing, already, had been digitalised. And the data matrix technology is not required when franking mail using non-permanent stamps.

Forever stamps are an investment if your definition of investment is not increasing in face value beyond the rate of inflation.

Right.
https://www.mondayeconomist.com/p/stamps
August 7, 2023
Why Stamp Prices Outpace Inflation
"... the price of postage outpaced the overall price level in the economy for decades ..."

I completely agree about Forever stamps being the best "investment" and inflation hedge. I also realize that no one can predict which subject material in non-Forever stamps will be popular in the future. However, are there certain non Forever series that come to mind from your experiences or opinion, where if one pays face value or over for certain sheets of a series or a complete set, that in the future it will retain value? Would Disney, Looney Tunes or Nature of America be some examples?

No.

You would be better off putting together clean used, non-FD cancelled, sets of all stamps issued in sheets with a different design on each stamp.