Why would you not provide an EPS for a logo? Tiffs from Ai are always flat and never transparent. Photoshop can save layered TIFFs, that's how they can be transparent there. Not possible in AI though. You could copy > paste into Photoshop and save as TIFF. PDF is also a very good format to provide. I always provide, ai, eps, pdf, psd, tiff, gif, jpg, and png for logo projects.
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