here is a list from several years back... Van Nuys is tops there as well:
Table 4.—The 10 Most Active General Aviation
Airports
a
Airport Annual operations
1. Van Nuys, CA . . . . . . . . . . . . . 590,758
2. Long Beach, CA . . . . . . . . . . .. 461,287
3. Santa Ana, CA . . . . . . . . . . . . . 396,029
4. Seattle-Boeing Field, WA. . . . .. 362,524
5. Oakland, CA . . . . . . . . . . . . . . . 334,557
6. Tamiami, FL . . . . . . . . . . . . . . . 301,363
7. Opa Locka, FL . . . . . . . . . . . . . .295,215
8. San Jose, CA. . . . . . . . . . . . . . . 264,936
9. Pontiac, MI . . . . . . . . . . . . . . . . .238,532
10. Melbourne, FL. . . . . . . . . . . . . .229,138