The regular 2 has a switch for resistor activation if you use arcade pcbs to tone down the video gain. The plus does not. The regular 2 also has better comparability with off spec sources (again, arcade pcbs) but it does crop some oddball video sizes down, so you might lose a bit on the top and bottom of the picture.
The 2 plus is basically the same as an XRGB-3 in terms of pure line doubling and options (tons of them). It doesn't cut any picture real estate off but it works only with somewhat standard video specs and it is produced a slightly less stable picture than the 2.