I, personally, chose the first Red Faction. It's one of my favorite multiplayer games ever.

I played the RF multiplayer demo for way longer than was healthy. Because of the ability to quick-switch between the assault rifle and the rail gun, incredible shootouts would emerge in the middle of blasted canyon (the only worthwhile map on it). I moved onto the full game but power-ups and the HMG (primarily) lessened the appeal, as well as lame stuff like click-modding.
That said, it's one of my all-time favourite multiplayer games as well.

Strangely enough, Red Faction II.

I chose the first one. Loved the story in it, and it really took advantage of the GeoMod in the first half. Multiplayer was pretty excellent, as well. That game just brings back so many good memories, and it still holds up today. The fact that no game before Guerrilla did destruction as good as the first RF really says something about it. 
 
Guerrilla is definitely my second choice. The main story and world is huge and the destruction and physics are very revolutionary. The multiplayer is also unlike any other out there and it's a crime that it only lasted as long as it did. Guerrilla was easily the most overlooked and underrated game of last year. The tech in that game alone is worth some good recognition that it just didn't get.
 
Red Faction 2 is...well, a good game. Doesn't come close to matching the standard set by the first, but it's still a very fun game. It's too bad the campaign's use of GeoMod was so underutilized. It was basically during all the scripted sequences. The MP in that game was the best, though. The maps were fun as hell, and the ability to create and customize your own bots is something that other developers should've picked up on at the time. The only bad thing about it was you couldn't make your own tunnels like in the first.

The hours I spent multiplayer in that first one, creating odd eloborate tunnels and blowing stuff up. So much fun.

Guerrilla, if only because the story was much more open and the buildings were much more destructible than the first two. There are fewer snipers getting cheap kills and fewer people using glitches to run up the score in the multiplayer.
 
Also, number 2 was a load of crap because they took away the multiplayer for a simple "bot match" mode, and way too many times the in-game cutscenes would have trouble syncing up the speech and the characters' motions. OTOH, it did have Jason Statham doing a small voice-over role before he became widely-known.

As much as I loved the first, demolishing building in Guerilla is therapeutic.