Seems this is turning into "El Rincon de Tequila" (Tequila Corner.) Maybe we should move this to the non-diving forum, but for now, I'll bite: Mexican Conmemorativo is an extra-aged anejo; they claim three years' aging vs. the standard 12 months. That's an A grade. However, beware of U.S. import versions that are not anejo, and may not even be 100% agave. The label will indicate both factors. If it's 100% agave, it'll proudly say so on the label. If it's not, I wouldn't apply it internally.
Non-100% agave tequila is called a "mixto". By Mexican law, it only has to contain 51% blue agave distillate. The other 49% can be ANYthing from other cactus distillate to cheap vodka, even (edited for accuracy) pure grain alcohol. You'll never know, because complete contents need not be labelled according to the law. (Added: meant grain alcohol, which has been added intentionally for extra "kick", but not the poisonous wood alcohol.)
OTOH, if it's not anejo but still 100% agave, that's fine. It could be "reposado" (literally, "rested"), which is aged at least two months. It could conceivably be silver -- unaged, although I don't think Conmemorativo comes in silver (maybe for the U.S. market.)
Aging creates different taste combinations by increasing the complexity of the taste. Silver has a simple cactus "bite". Anejo has a rainbow of flavors including citrus, vanilla, and more, depending on the barrel in which it was aged. Your choice of silver vs. reposado vs. anejo is just that, your choice, as long as it's 100% agave. If it ain't, have something else. Anything else.
As long as I'm holding forth from my bar stool, er, my work desk chair: the worst mixto of all time is Jose Cuervo Gold, the favorite in movies and frat parties. It's an abomination, not least because it includes food coloring. Sauza even has to compete by offering their own "gold" product, their only mixto, which also includes food coloring. Although anejo is colored by aging, no natural tequila is ever that shade of gold.
Salud! (which is actually the first word of a great toast that goes as follows: "Salud, pesetas, y amor, y tiempo para gozarlos." That translates to: "Health, money, and love, and time to enjoy them.")