That’s an easy one. My favorite card game (with a standard decks of playing cards) is ‘Casino’! It’s really hard to find people that know how to play. It’s a quick-paced game, but not so brain-bending so it still allows everyone to socialize a bit. Games can be relatively short or long depending on which version rules you decide to use. An awesome game even school children can play to help strenghen their math skills. Highly recommended.
Complete official rules here:
For ANY type of card game, then my favorite is ‘Phase 10’ (pictured above). It’s basically Shanghai Rummy with a different deck, if you know how to play Shanghai. A description and rules are here: