To clear in, there's a choice of two locations. #1. 'Jetty Point' on the SE side of the island, beside the Royal Langkawi Yacht Club, or  #2. Telaga Marina, on the NW side, which is part of the Telaga Harbour Park complex. (See full details in "Clearing In and Out"). At  both locations there's also the possibility of taking a mooring or free anchoring. Firstly, here's a summary of the three marinas in Langkawi, followed by details on moorings and anchorages.

Marina Pros and Cons:

RLYC (Royal Langkawi Yacht Club)
Pros Near to Kuah shopping facilities. Fuel dock for diesel only. WIFI.
Cons Despite a new sea wall, there is still some swell from ferries.
Pros Nice open scenery. Choice of several restaurants.
Diesel & petrol at fuel dock and also at Petronas Service Station.
Customs, Immigration, Harbour Dept on site for check IN/OUT.
Cons Very limited shopping facilities - only for daily use.
No public transport. You need to hire car or taxi for provisioning.
REBAK Marina
Pros Pleasant surroundings. Very quiet. Use of pool & choice of restaurants.The only marina with haulout/hardstand. Some chandlery on site.
Cons No diesel or petrol. No shops. Need to use free ferry for 15 minute ride to
Lankasuka jetty, then hire car or taxi for provisioning in Kuah or Padang Matsirat.