Batting average tells you how often a player gets a hit in plate appearances when he doesn’t walk, get hit, voluntarily give himself up, or happen to hit a deep flyball with a runner on third and less than two out. Unless that runner isn’t very fast, in which case the hitter gets penalized. Also all hits, be it a slow roller down the third bad line that the defense hopes goes foul, or 460-foot blasts that clear the entire ballpark, count the same.
OBP measures how often you get to 1b by offensive means. It does treat walks like home runs
SLG is BA but credits doubles, triples and home runs.
OPS credits the batter for reaching base, treats hits based on TB, and either mitigates or eliminates the flaws in BA.
Of the 4, BA just tells you the least about a hitter…