Most of the SSTV programs I have worked with will auto-select the correct mode upon reception.
Scottie 1 and Scottie 2 are probably the most common formats out there, with the Martin and Robot formats making up probably 95% of the remainder. I have heard some quick squirts of the 8- and 12-second B/W modes, and a handful of Scottie DX transmissions, but Scottie 1 & 2 are probably your best bet for receiving.
In your software, load up a few sample images and "send" them without anything hooked up to the sound card but your speakers. This will give you a feel for the timing and cadence of the formats, and after some practice, you can sort of judge between them by ear.
If you're using MMSSTV, set it for auto-start, and make sure that the "auto" button is selected in the format list. With any signal strong enough to have a definite sync pulse, it should be able to auto-detect and receive it on its own, without having to worry about manual mode selection.