What is the best Fenix 5 or Garmin 245?

They are equal

It depends on what you plan to use it for. The 245 does not have multi sport or open water swim modes, so if you intend to do triathlon, duathlon, etc the Fenix is a better choice. On the other hand the 245 can be had with music support.

I'd suggest using the DCR Product Comparison Tool here to see what the differences and similarities are: www.dcrainmaker.com/product-comparison-calculator