98 and 100 square inches are the two sizes almost the whole modern market sits in. The difference sounds trivial and is not: a bigger head has longer strings, so the bed deflects further on impact and returns more energy, and the sweet spot is both larger and further from the hand.
In our own scoring model, head size is the single biggest input into power and the biggest negative into control — every square inch moves power up and control down by a fixed amount, which is exactly the trade the two sizes represent. The model is published in full on our How we score page, so you can check the arithmetic on any frame.
In practice: a 100 in² frame is more forgiving on the ball you did not quite middle, and it gives free depth on the defensive ball you had no time to swing at. A 98 in² frame gives up some of that in exchange for a ball that goes where it was aimed, which matters more the harder you hit.
The complication is that head size never travels alone. A 100 in² frame at 300 g with a 16×19 pattern and a 300 g 98 in² with an 18×20 differ in three ways at once, and the head size may be the smallest of them. Read the pattern and the weight in the same glance.
If you are choosing between two specific frames rather than two sizes, put them in the comparison table: it shows both on all six criteria, and the row that actually separates them is usually not the one you expected.