There are a lot of options. It mostly depends on what you want to do and how much money you want to put away. If you are not fully funding an IRA and want to save less than $5500 a year (depending on age) then an IRA is the way to go. There are several other options for someone self employed who needs or wants to save more than this. I personally use a SEP IRA. I chose that because it was very easy to setup using ETrade, where my IRA and regular brokerage accounts are. It lets me save 25% of my profit pretax. A Simple 401K seemed to be a bit harder to setup and 25% was enough for me.
Back to the IRA thing. If you are saving less than $5500, an IRA is a MUCH simpler way of doing it. Let's say you make $20,000 a year after all of your deductions and you want to save 25% of that ($5000). With an IRA you simply put your $5500 in and boom your taxable income is now $14,500. With a SEP you do have to figure separately your contribution limits (I let my tax software do that). Let's say you only make $19,816, now you can no longer save your $5000 but now instead can only contribute $4954. If you go with a Simple 401K then now you have to figure what part is your employee contribution and what part is your company contribution and holy cow then it gets crazy weird with lots of things you now have to keep track of as long as you have the plan.
There are reasons that a body stays in motion
At the moment only demons come to mind