Well first of all the bulb shouldnt be kept on 24/7 because constant light isnt good and the night time temperature can drop.
But as to pros and cons of both.
Bulb:
Pros- heat is radiated downwards to the snake which replicates the sun
- dont need a thermostat
- cheap only around $10
-makes the ambient and basking temperature the right degree
Cons- the bulbs sometimes go out really fast
-drain humidity and dry up the tank
- can burn your snake if it is touched
- alot of electricity
Heat Mat:
Pros- Provides the snake with belly heat
- Better for when the snake is digesting
- Some heat mats are inexpensive
-Last a while
-If used with a thermostat it can stay at a constant temperature
Cons- needs to be run with a thermostat which cheapest can start at is $30
- WILL burn your snake if used without one because they cannot tell its that hot
-Will not warm up the ambient temperature to the degrees required unless using a tub
Both have their pros and cons, i personally use the heat mats for my snakes in the tubs, and the bulbs for the snakes in cages. But i will be switching over to heat panels since they are alot better even though expensive .