When you say loop we're thinking of custom loop, which can only be done for £100 if you go second hand tbh.
h100 is an all-in-one 'water' cooler. Basically just a fancy heatsink. Temps are in the same ballpark as a top-end air heatsink.
h100 pros:
-temps are good (not as good as proper custom)
-opens up the board aesthetically (can see more etc)
-can buy ram with nicer looking heatsinks
h100 cons:
-already more expensive than similarly performing air heatsinks, yet requires purchase of 2 aftermarket fans because the stock ones = jet engine
-reliability of pumps can be an issue