The one great thing about an SEP IRA is that the contributions are not subject to Social Security taxes, like contributions to traditional individual IRAs are. Add to that the fact that, as your own employer, the combined employer plus employee Social Security bite on your gross revenues is upward of 12%. And what you get is a situation where, on the same gross revenue, your contribution to an SEP IRA ends up being much larger than on a traditional IRA. And the limit on how much you can contribute is much higher.
Double check this for yourself on the IRS website. But, when I had the same question you have, the above is what I concluded.
