I use spot bulbs as that was what my first viv came with. Have since fitted them to two others.... up side, gives light by which to see your snakie friends (I use red bulbs).... down side, bulbs blow every few months and are not the cheapest to replace, but do not get them from Reptile shops, go to ordinary electrical shops... also have to use a dimmer stat, which is slightly more expensive... all things considered though, still like them. Use heat mats in two smaller vivs for smaller snakes, and these appear just as effective. So, possibly personal preference, dependant on area required to heat and what is best for husbandry requirements of animal.
Good luck with whatever you decide... J
My mind doesn't just wander.... sometimes it leaves completely!! Horace Hornblower & Tango (gone but not forgotten)!