Why? Because they are next to the glomerulus, of course!
"But Elena," you say questioningly. "Who cares? Why would that make them your favorite?"
Well, let me tell you. 'To juxtapose' (loosely) means "to place side by side" - so then what does juxta-glomerular mean? It's an adjective meaning next to the glomerulus! And wait, someone remind me where the juxtaglomerular cells are... THAT'S RIGHT, just next to the glomerulus. Love it!
[If we wanted to take this one step further (which we do), they should really be called the renin-secreting juxtaglomerular cells - because then I could also remember what they actually do, not just where they are. But hey, I'll take what I can get.]