That's a good question.  Lately I'd lean toward sidescroller, but it's hard to say.  Maybe some other people can chime in.

If nobody else says anything, I'd say just take your pick. :)

I love playing games in either style. That being said, having top-down resources is always a plus (personal preference). I'm not an artist but the Dawn Bringer palette seems quite useful and popular, you might be able to make whatever resources you craft compatible with a larger set by using that palette.

http://www.pixeljoint.com/forum/forum_posts.asp?TID=12795

You can find the original post by Clint Bellenger about this palette here:

http://opengameart.org/forumtopic/texture-examples-using-dawnbringers-16...

Here is a discussion that includes some 32 color palette talk:

http://opengameart.org/forumtopic/lpc-assets-dawnbringer32-palette

And finally, here is a discussion about color palettes that includes some talk about the same:

http://opengameart.org/forumtopic/colors-and-palettes

I agree top down style is typically more useful, for me.

And, it's possible to do more with less tiles.

I forgot, here's a direct link to the DB32 palette if you so desire it:

http://www.pixeljoint.com/forum/forum_posts.asp?TID=16247