Is it more advantageous to go for a graduate degree right or pursue a 2nd Bach?

If your aim is to be highly educated among your peers and have an additional degree on your resume go with the graduate degree. In terms of looking qualified for a desirable job it is usually better to be a specialist than a generalist. Aim for a graduate degree that mixes the field you prefer with elements of the 2nd under-grad you wanted to be exposed to. Cheers.