I love this, but I'm really not sure whose version I should pick up. Is somebody's considered the definitive performance?

That’s a pretty good question, unkempt; that surely is one of the more popular pieces of music that people still love. I believe that there are over 25 million recordings of this orchestral work but I will try to recommend some. But no, I don't believe there is a "definitive performance."

Vivaldi: The Four Seasons, etc. 1997, Gottfried von der Goltz and the Freiburger Barockorchester (Andrew Lawrence-King, director) This is a good one to get because it is packed with music and the orchestra truly sounds superb.

Somebody once told me that the Decca collection of Vivaldi’s work is not very good. Not because the music isn’t good—not at all, Vivaldi was a great composer—but the performances aren’t good. Very dry and phoned in.

You know, to be honest, most of the performances you find are going to be great. You should be able to find a used copy fairly easily. I have a vinyl version of it but I can’t think of the performers right now because I am at work. However, even that would do. You could just buy a used CD of it for about $3-5 and if you don’t like it, get another version. But if you truly adore that work of his, then order the aforementioned one—its pretty fantastic.

I haven't heard the Lawrence-King version yet. I'll have to look into that. "Four Seasons" is a superb piece of aural bliss.

My favorite version is by Nils-Erik Sparf and the Drottingholm Baroque Ensemble, not exactly a household name, even in the world of classical music, but this is a great performance that has been acclaimed since it came out in the 80's. The slow movements are beautifully lyrical and the fast movements are the most exciting on disc. Plus, this is an "authentic" recording, meaning that it has been performed the way that Vivaldi intended (or at least the way that we think he intended) and with the instruments that Vivaldi specified. Some recordings, particularly those made before the 80's and those on budget labels might actually be "modernized" versions, played with different scoring and modern instruments. One disadvantage of the Sparf disc is that it only contains "The Four Seasons" and so the disc only clocks in at 39'36. Plenty of room for another piece.

Actually, I sometimes prefer a disc to have just the one work if it's substantial enough. Seeing as my iPod is on the fritz (i.e., practically dead), I've been using a portable CD player everywhere I go, which sucks. And, when I get involved in a piece, I like knowing that that's all that I'm going to hear in that specific chunk of time and not have to dig for my CD player in my bag to turn it off right when it ends. Then I can just sit and absorb what I've just experienced for a while.

I think I'm taking this whole thing a tad too philosophically. Sorry about that. But yes, I'll have to get the Sparf version as well. Is it very difficult to find?

The Sparf version is around. I did a search for "Sparf four seasons" and it was on sale at a few different sites.