2d vs 3d avatar creation

The 3D system will have a greater upper bound on permutations and variations. It's easier to mathematically deform a mesh to create new part variants, and then swap in parts while maintaining overall visual consistency. You can also blend textures and perform other computations to give the generated avatar visual coherence.

For instance, if you have a raster image of a torso and a collection of selectable arms, you won't be able to use the really hefty, muscular arms with the big shoulders along with the slender torso unless you're prepared to have an awkward transition at the shoulder. In 3D you could scale the shoulders down slightly and scale the chest and neck areas of the torso up slightly to create a better match.

Finally, you can still use a 3D avatar creation system in a 2D game. Once the player is done designing their avatar, simply render it out - you can even render sprites at precomputed angles, if you want (I know of an entirely 2D game written in Adobe Flex that does this for performance reasons, rendering the user-configured "paper doll" avatars into sprite sheets for runtime use) . A 3D avatar creation system clearly has the edge in terms of flexibility and range.

A 2D avatar system on the other hand is easier to create with volunteer labor, you can get nicer-looking results with less talent (even some professionally made 3D avatar systems are ugly as sin), and if you don't want a system with a lot of animations, the 2D method takes fewer man-hours.

Gaia Online is one of the best examples I know of a 2D avatar system with some basic animations and thousands of customizations; the system is mostly loved by players, some will spend hours making 'dream avatars' at tektek.org. There are a few a few complaints about the system that could be easily addressed in designing a new, similar system. Those objections are:
- a lot of people would prefer less chibi-looking characters, or more basic body types (Gaia has only two, male and female).
- The original system should have been designed to allow players to control the layer order of items they were equipping
- Items should come in a standard range of colors, or each item's color(s) should be player-selectable at the equippage screen.

great answers, thanks.

The animation will be limited to walking in the cardinal directions. I would like the style to come out pretty strong, so 2d seems to be what I'm looking for.
I'm not looking forward to doing three animations for about 100 outfits though, oh well!

Sean

Well, what you do is you have all the animated poses of the character base squished into one transparent layer. Then you draw all the poses of a single article of clothing over top of that in the next transparent layer. (Or you can print out the base sheet, put it on a lightbox, put a clean paper over top, and draw the clothing onto the new sheet.) So unless you want a cloak that whips around in the breeze or something, animating the clothing doesn't usually take too much thought. It does get a little more complicated in the case of a single article of clothing which exists on more than one layer.