I'm a big fan of "older" daylilies, too, and for much the same reason - their sheer vigor, when it is present, is astounding. But, there are weaknesses and drawbacks through all stages of DL development right from species forms and onward.
Garden daylilies, I think, is a term often used to reference Species and Heirloom daylilies - those that are less removed from the "wild" ancestral line/s. Even back then, there are some that are noted as being more or less good performers, and are more or less suited to today's gardening needs and widespread growing conditions.
Hemerocallis dumortieri, for example, has been noted as being susceptible to rust, and it may be that some of our modern DLs have inherited similar genes that originated even farther back than dumortieri.
On the other hand, Hemerocallis citrina is noted as being resistant to rust, and likewise, many modern DLs may have inherited its strengths:
Some of the older forms can also be very "vigorous" or even "invasive," sending their roots far and wide (killing off other desirable garden plants) and proliferating so quickly and persistently that many home growers would find them unsuitable. AHS maintains this bulletin about the differences that indicate "invasiveness" in DLs, using Hermocallis fulva as example:
http://www.daylilies.org/AHSin...
Fulva, noted as both invasive and susceptible to rust:
Other than that, it becomes much more complex and subjective to identify "recommended" cultivars. So, it can help to define, for yourself and for others, what attributes are important to you. The more characteristics you find and describe that are important to you, the easier it is to identify cultivars. Ruffles? Complex patterns or edges? Lotsa blooms or more time blooming in a season?
Selecting and describing goals, even very specific attribute goals, for the DLs you'd enjoy having in your garden is a sure way to maximize the chances for others to call up recommendations that may astound and please you for many years to come.