If you plan it to use it with a sound board you will probably be ok with almost any momentary (non-latching) switch you can find, for Obsidian/Diamond boards i think the switch pin basically just detects if you connect it to the battery minus and for how long, the actual power that feeds the board is through the battery+/- pins > this means no significant current goes through that switch. For switches usually the rating is max current at X voltage - the 3A at 250V AC means you can use it in an AC setup of up to 250V with a current of up to 3A (and you want to have these values larger than your predicted current); switches with led(s) built in (illuminated switches) also have a rating for the led(s), something like 20mA 6V DC(or 12V, or 24V).
Now that being said, you might have some problems with some switches (e.g. very large or very small ones) due to some of their other properties (some of which aren't even listed in the specs) like internal build structure which affects the resistance (the switch acts like a very small resistance) or the way it establishes the physical connection (affecting the de-bounce time) - maybe in other ways (you need to ask an electrical engineer for more details). To be 100% sure you need to ask the manufacturer of the board you are using or you need to actually test it with the board.
But, as I said, you will probably be fine with almost any momentary switch and as a general rule of thumb if you can choose between two switches similar in size/build and price
but with different ratings, choose the one with higher ratings (more V or more A).
If you use it for a stunt or in another similar setup, with a latching / non-momentary switch then you need to take into account the current your setup draws (which in this case will pass through the switch). For example you need at least 6V at 2A to be on the safe side (a LED die usually draws 0.7-1A); but aim as high as you can get away with (cost/size/design wise) for the switch specs (more V or more A).