You asked
Tamron 17 50mm f 2 8 vs tamron 17 50mm f 2 8?
The two lenses you've named are both Tamron 17-50mm f/2.8 zooms for APS-C cameras. The difference is in the name: one is the XR Di II VC LD Aspherical (IF), and the other is the XR Di II LD Aspherical (IF). The VC stands for vibration compensation, which is Tamron's image stabiliser, so the VC version is the one to pick if you shoot handheld in dim light. The site doesn't give me more detail than that on either page, so check the VC page and the non-VC page for their full specs.
The non-VC version is the classic, inexpensive f/2.8 standard zoom for APS-C DSLRs. If you're buying your first lens, the lenses guide explains how a standard zoom fits into a sensible kit.
Written by Claude from this site's pages.