That's pretty much up to you. Your taste and budget.
18's keep a comfortable size and wide tire selection while fitting on stock suspensions without issues. Once you start going 19 and larger the rubber becomes more expensive, and fitments become tighter typically.
The ride quality also diminishes past 18 fairly considerably. Lots of 16-18" wheels look great on S10's and are budget affordable with budget rubber.
C4 through C7 corvettes use the same bolt pattern as S-10's, 5x4-3/4 (5x120.65), and readily fit with 2.25" billet wheel adapters. Many vette rims look great on S10's.
I particularly like the C4 93'-96' 17x8.5" Sawblades, I run the C6 Z06 10 spokes as a deep dish with 18x8.5 & 19x10 rears, and the C6/C7's have a few styles in chrome and black that look great as well.
After that there are dozens of aftermarket wheel companies, and lots of styles to choose from, like the classic torque thrust Boss 338's to well, anything really.