TIF would be a good idea, as long as you're not planning to distribute it. But TIF's are huge compared to png, so to make smaller downloadable files, png is better :o)

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You just can't put the words "Poserites" and "happy" in the same sentence - didn't you know that? LaurieA
  Using Poser since 2002. Currently at Version 11.1 - Win 10.