Although others here have said that it is impossible to like one volume of "69 Love Songs" over any other, I fear that it is. This is, currently, my favorite volume.
There are just too many good songs on here -- "Roses," "When My Boy Walks Down the Street," "Time Enough For Rocking When We're Old," "Very Funny," "Grand Canyon," etc, etc. And "Papa Was a Rodeo," "Epitaph for My Heart" and "Asleep and Dreaming" are some of Merritt's best compositions, lyrically and musically.
Sure, it sort of drags a little bit in the middle ("Washington, D.C." and "Kiss Me Like You Mean It" come to mind), but all three volumes have their share of somewhat mediocre songs.
It also has the best opening and closing tracks of the three volumes (although "Absolutely Cuckoo" is pretty amazing) -- "Roses" is a lovingly sung thirty second song that defies catagorization (there's no music, just a beautiful voice); and "I Shatter" also defies catagorization with it's Laurie Anderson-like vocals (anyone remember that oddity "O Superman"?).
Regardless, you should not just buy one or two volumes -- buy the box set. There are some songs ("Absolutely Cuckoo," "A Chicken with Its Head Cut Off," "Busby Berkeley Dreams," "The Death of Ferdinand de Saussure," and many, many more) that are not available on volume two. But, if you must buy one, I guess I'll be one of the few to say "pick volume 2."