When players ask "What is the best poker hand?", they usually mean one of two things: the best 5-card showdown hand (The Royal Flush) or the best 2-card preflop starting hand in Texas Hold'em (Pocket Aces). Here is what you need to know about both.
The Royal Flush (The Unbeatable Hand)
An Ace-high straight flush composed of A-K-Q-J-10 all belonging to the exact same suit. It is mathematically the rarest hand in poker, occurring once in every 649,740 five-card deals.
Pocket Aces (The Best Starting Hand)
Known affectionately as "Pocket Rockets", "Bullets", or "American Airlines", a pair of Aces in the hole is the most profitable preflop holding in Texas Hold'em.
Against a single random opponent, Pocket Aces is an 85% favorite to win at showdown. However, multiway pots (with 4 or 5 callers) reduce the equity of pocket Aces to roughly 35-40%, which is why raising aggressively preflop to isolate a single caller is critical.