I collect. I swap spares with people, which is lots of fun if it's with people all round the world. I need to sort out my collection actually, because I've lost count of how many I have now. I have a huge box full of them which I can barely pick up now. I used to keep a spreadsheet, but... yeah didn't keep that up.
I've bought a few, all old ones. The best of which is a 1991 Lightwater Valley map with an awesome illustration of the Ultimate on it. I payed £2 for it. Well worth it!
I sell spare maps on ebay, and it's surprisingly profitable if you can be bothered. The other week I sold a Universal Orlando map for £9.50 to someone in Spain. Most go for 99p-£2. There's a couple of people who've regularly bought maps from me.
As for favourite map, I think it might well be Cedar Points. All of Cedar Fair's maps are lovely, but Cedar Point's is really nice. Parc Asterix had an awesome one a while ago that folded out in the most unusual way. Alton Towers have had some amazing and some hideous maps.