I've had plain 'ol Gabriel gas, Koni, KYB Gas a Just and KYB GR-2.
If you want a stock ride type shock, the KYB GR-2 are hard to beat. Firm and controlled, but not stiff. About $15 each
Gas a Justs are firmer valved. Some find them too stiff for the rear. One issue is the front shock they spec for the 71-73 Mustang is an inch too short. You need to get the 70-71 Torino shock # 4505, it's a little longer, and the same length as the GR-2 for the 71-73 Mustang. About $30 each.
Konis are a very nice single adjustable hydraulic shock. Only problem is the 71-73 front is no longer made. IIRC, you can get them made by Koni's custom shop, or you swap the 65-70 shock tower cap and use those. They have a new series called STR.T that's a mid price shock.
Bilstein is another popular choice, they are custom made by RCD and available from Street or Track and Opentracker Racing. They come in several different valving options.
There are others avaialbe, such as Viking, QA-1 etc, but I have no experience with them.
RockAuto link for KYB shocks
https://www.rockauto.com/en/catalog/ford,1971,mustang,5.8l+351cid+v8,1132692,suspension,shock+absorber,7556
Torino front shock -
https://www.rockauto.com/en/moreinfo.php?pk=502712&cc=1141074&jsn=3450
Link to Konis for 65-70 front and the STR.T shocks
https://www.teambeefcakeracing.com/koni-shocks-1964-1973-mustang.html
Link to Opentracker for Bilsteins - about half way down, they also have Koni, Viking etc.
https://opentrackerracing.com/product-category/shop-by-year/1971-1973-mustang/