300x250 vs 336x280 in-content

300x250 vs 336x280 in-content
The 36 extra pixels matter more than you'd think. Both are 'medium rectangle' but 336x280 pulls a slightly higher-value ad pool and just fills bigger in the reading column.
Problem: 336 breaks layout on narrow content widths and looks cramped on small phones.
So: responsive in-content (lets Google pick, usually grabs the 336 when it fits, falls back to 300 when it doesn't). Only hard-code 300x250 if your column is genuinely tight.
Let responsive do the sizing math.
Test it on one page first.