I cant comment on mercury vapours because ive never used one, but i do use the tried , tested and true combo of linear flourescent UVB and incandescent basking lights. They work well and I don't see a need to attempt to improve on that solution.
I have seen debated, the issue of combining basking heat and UVB light in one single source. At particular issue is the arguement that by providing both together , the cham is not afforded the choice to seek heat alone or UVB alone. Clearly, food for thought ...