Sydney in 4 days & Airport shuttles
 

Visiting Sydney in May 2018, any recommendations on airport shuttles. I've read so many reviews I'm confused and think maybe it's better to book when i arrive.
Any suggestion on what we can do in 4 days> Visit to Blue Mountains a good idea in month of May?

Avoid Sydney airport shuttles like the plague!
 

Sydney airport - CBD shuttles are an embarrassment, with a well deserved appalling reputation for unreliable service.

Depending on (1) the number of people & luggage
(2) location of your hotel - take the airport train or get a taxi from the rank outside the airport terminal. If you use Über, that’s available, too.

There is is no need to pre-book taxis.

As for what to do in 4 days - depends entirely on your interests. The usual things are visits to the Opera House, The Rocks, a trip to Manly on the ferry, a walk across the Harbour Bridge, or perhaps a Bridge Climb, Taronga Zoo,Royal Botanic Gardens, Museums & Art Galleries, Harbour & coastal walks ... whatever it was that attracted you to Sydney in the first place. All of which you can look up online, at Sydney.com

With 4 days, you certainly have time for a visit to the Blue Mountains. May can be a great month to visit. Keep an eye on the weather forecasts on TV or on www.bom.gov.au for the Blue Mountains to choose the best day to go.
You can take a train ( 2 hours), drive ( about 90 mins) or do a day tour.

If you haven’t already booked your accommodation, www.booking.com is a good resource. I usually use it to find accommodation - then book direct with the property.