My income (like a lot of people who do tech startups) is variable between $0-40k/yr (pre-funding, etc.) and $150-300k (high paid consulting, post-acquisition, etc.).
What I do is 401k and SEP IRA (and defer) as much as I can during the high income years (and pull forward expenses), then convert it to Roth IRA during the lean years, to take advantage of differences in marginal rate. The goal being to get it all into a Roth as soon as possible at an overall decent rate.
Roth gets you forever compounding, and tax free dividends and other gains, and no taxes on distribution, which is basically ideal.
Deferring taxes is generally preferrable unless you plan of retiring very soon. Mathematically, the amount you save by deferring taxes now can equal up to nearly 20 years of earnings growth, or more at today's low interest and growth rates.
With currently-taxed contributions you don't have to worry about future taxes...but you start off with a substantially smaller base. You also take the risk that future taxes won't be lower than they are now, or that even if they are higher that retirement withdrawals will not be subject to special taxation regimes.
What I do is 401k and SEP IRA (and defer) as much as I can during the high income years (and pull forward expenses), then convert it to Roth IRA during the lean years, to take advantage of differences in marginal rate. The goal being to get it all into a Roth as soon as possible at an overall decent rate.
Roth gets you forever compounding, and tax free dividends and other gains, and no taxes on distribution, which is basically ideal.