ER
Worth 2 points before any premium square, and the lowest-scoring of the 96 — tied with 35 others.
ER extends into 10 three-letter words, which is the 45th most extendable of 96 — tied with 8 others. That is the number worth memorising: a two-letter word is a place to put tiles, but a well-hooked one is a place to put them where the board stays open.
Every hook
- F→FER
- H→HER
- P→PER
- S→SER
- A→ERA
- E→ERE
- G→ERG
- N→ERN
- R→ERR
- S→ERS
Not all of them are equally reachable, which a bare count of 10 hides. ER hooks on 9 distinct letters, and the ones you are likeliest to be holding are E (60% of opening racks), A (49% of opening racks) and N (36% of opening racks). The rarest is P, at 14%.
How often you can actually play it
Out of an opening rack, 20.15% of the time you hold the letters for ER outright, the 4th likeliest of 96 — tied with 4 others. Counting a blank as whichever letter is missing lifts that to 27.80%, though spending one of the two blanks on a two-letter word is rarely the play. Exact hypergeometrics over the 100-tile bag, not a simulation.
It reverses
ER backwards is RE, which is also good. That is how most of this list is actually learned — 46 of the 96 come in reversible pairs, so knowing one gets you the other free.