I agree that a .22 can is the best first purchase. I have a couple of different calibers but I shoot the 22 the most.
Also, a screw on can works good since you can switch it between multiple guns
without difficulty.
My only ther suggestion is to look for a suppressor you can take apart.
I shoot almost exclusively subsonic ammo.
That has the very real tendency to foul/lead up a suppressor quickly, especially if you shoot semiauto or full auto.
I have a sealed .22 suppressor and I have tried everything under the sun to try to get it out, including a subsonic bath overnight, and the only thing that works is to smack it against a piece of wood to break it loose and then shake out the chunks.
Adding water or anything else increases the rate of fowling dramatically.
Before everyone freaks out my can is made of titanium so DO NOT TRY THIS WITH AN ALUMINUM CAN!
I do this at my own risk and take full responsibility.
I have shot other integrally suppressed .22's and they may be a little more quiet than a screw on can but I have found this difference to be marginal at the most.
Remember that any suppressor will cause a semi/full auto gun to get dirty fast because of the back pressure through the barrel/action.
I have found that remington subsonics will cycle very reliably in my 10/22, all others have routine cycle problems.
Hope this is helpful.