Well I already have created .3DS loader, but i have read that it's old and have a lots of limitations... That's why i'm asking for any good model type. Like i already mentioned i want it to be able to represent character animation. Skeletal animation specificaly
Those two programs will create models that have skeletal animation. 3D Studio Max has its own type and Milkshape will save into a variety of formats. I suggest checking the list of formats it supports and pick a nice open standard one (easier to create/find a loader that way)
Blender is a pretty good editor and it supports many formats.
The world of 3D file-formats is seriously lacking a wide-spread standard format. It used to be 3ds, when only 3D Studio Max existed as a decent editor. Now, there are many 3D editors, many formats, and most game-studios have in-house formats too.
For the kind of thing you are looking for, you might want to use X3D. It also has some open-source libs to manipulate them, but since it is an XML format, you can also just use a generic xml library.
Well i don't really like XML format models, because they consume much more space than binary. So i was thinking about making a converter from X3D to my own format wich would contain all X3M model data exept XML tags would be changed to binary identifiers... Is it worth doing that? Or maybe there is some other model format wich would suite me better?