I think they both have their strengths. I started off as a chat RPer, and I dabbled in normal forum RP for a bit, but could never really get into it. I found that the way a lot of chats were structured with channels reflecting different parts of a town or map made stories flow more easily between rooms, though this isn't always the case with all chat environments.

The major benefit that I've seen with forums, however, is that it is much easier to construct one for yourself and change code so that it suits roleplaying better. Features can be added without having to worry about server communication and all that, so you can come up with a much more dynamic environment. Of course, that's only if you're speaking from the perspective of someone who looks to create worlds as much as participate in them.

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Small, brown, moderately hairy, lightly spiced. Just how mom used to make e'm.

Creator of Anathema Online, a hand-coded text-based world built from scratch specifically to cater to freeform roleplayers, with features galore to bring a sense of tangibility and realism to the glorious genre spawned from the age-old tradition of descriptive literature.