What is closer to the Airport and how long , Sliema,Bugibba,St Pauls B

none of them
they are buses to all those places from the airport but your looking about 50-1h 30 min journey

the x3 serves bugibba and qawra  and the x2 does sliema and st julians

How will you get there?

By car/taxi: about 20 min if no traffic and if there is, god knows.

By bus:
X2 from Sliema and St Julian's  (1 hour)
X3 from the other three (1.5 to 2 hours depending where on route)

Since the journey time is so variable and since busses don't stop when full, you can't totally rely on published bus  schedules. Give yourself plenty of time. Plan to be at the airport at least 2 hours before your flight departure time, just in case the bus doesn't arrive or stop (both do happen occasionally).

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Qawra, Bugibba, SP Bay are within walking distance of each other and in fact it can be difficult to be sure which you're in. Same goes for Sliema and St Julian's.

None is within walking distance of the airport, so mode of transport matters. That said, Sliema is the closest.
If you want to be as far away as possible, either will do nicely: only Gozo is worse for the airport access.
Daily commute by bus is a big headache as time taken can vary enormously.

Ok thank you I am booking my Hotel today but dont know what one out of Sliema,Bugibba,St Pauls Bay or St Julians as I will be traveling to Birzebbgia, Pretty Bay so wonted to know whats closer,

Thanks,Alfie.

Easiest to stay and travel from Sliema if going to Birze. More buses and closer.
Look on a map and it should be clear which is best.