Do any CAGs still play? At least 1 of us does
Would I suggest it? Depends on your tastes/expectations
Which chapter is better? I like the story of Factions better, however the addition of Heroes you get in Nightfall is a global gameplay bonus too great to be overlooked. Factions grants you access to Alliance Battles which is some of the most fun you can have in PvP imo. Its a tough call. I found Nightfall to be rather boring as far as environments and storyline go. Didn't care for the two classes it added either, but like I said, the addition of Heroes is major to the game. Its like having 3 henchmen you can fully customize with skills, gear, stats, etc. you also can order them individually where to go on the map, and you can manage all their skill usage if you so choose.
That said, if you're getting Guild Wars Platinum to start with, you'll also get Eye of the North, which includes its own heroes.
One more thing to consider. The game is winding down some now. You'll be doing many of the missions on your own in the Original Guild Wars as well as Factions, simply because the people who still play have long since beaten the missions and have moved on to other things like PvP or High-end pve areas. Nightfall still has a decent number of players in it.
I'll be happy to play and help you out when I can, but its gonna help to make a few friends or join a guild that specifies in PvE stuff at least when starting out.