Which DLC is the best?
I'm leaning toward the British Forces DLC from what I've read so far. I only can afford one ATM so I would like to hear opinions.
Depends on what you're looking for. I'd personally get BAF as I play multiplayer almost exclusively and the BAF content is pretty widely used. If you mostly play MP, you will essentially be buying the DLCs for better quality textures and models, as BAF and PMC lite versions are included in Operation Arrowhead patches. ACR lite will not be included in a patch though, players have to download that separately. This means ACR content will be less used in multiplayer, as using it will shut out everyone who hasn't either bought ACR or bothered to download ACR lite manually.
My opinions, with the DLCs ordered best to worst:
BAF content is probably most commonly used in multiplayer, and it also has the strongest singleplayer campaign. If you play lots of MP, and even if you don't, BAF will give you most bang for your buck.
PMC content is mostly "cool" guns and vehicles and thus not too common in MP, and the campaign occasionally feels like they wanted to make a cool modern action shooter game without succeeding too well, instead of playing the engine's strengths.
ACR models are good but they suffer from quality control issues, as does the campaign (lots of bugs, misspelled text etc). The included maps are cut-outs of Chernarus and Takistan, the Chernarus cut-outs are retextured to be greener but the vegetation models suffer from unsightly LOD flickering. They also lack town logics (names, place definitions) which means they can't be used with many dynamic missions. The campaign doesn't have any coop support.
Clips are fully loaded, and then blood floods the lawn
Secondary Hivemind Nexus
BAF also includes quite a few neat singleplayer missions on top of the short campaign (Including the all time favorite Steal The Car mission) - It's the only DLC worth getting IMO.
So far... I guess its BAF too.
BAF is good, but so is PMC. The campaign is a bit different, but still fun. ACR is kinda lame, though.