How easy is it to get from the prague airport to downtown? What did you find to be the easiest?
Prague bus 119 from Airport to end of line (Dejvicka), takes about 25 minutes, where you will transfer to Metro A for 3, 4 or 5 stops depending on where you want to be in the Old City (or New City with additional free transfer at Mustek to Metro B). Or if you want Malastrana transfer to Tram 20 (but check for re-routings) instead of Metro at Dejvicka. Full transit ticket is 32 Ck which is about $1.60, available at stand inside airport, as are bank-owned ATMs.
The easiest is to go by taxi. You can buy your taxi voucher for fixed price at the airport hallway (about US$ 25), AE bus (Airport Express) will take you to the Main Train Station in downtown for about 3 US$. There are also minibuses taking you to different spots in downtown. Bus 119 to metro line A station Dejvicka. Bus 100 to Metro line B station Zlicin. Certain hotels and pensions have their own transportation which you can order. For more detailed information google Prague airport transfer and Prague airport public transport.
If you don't want to go by public transportation (which can take about 45 minutes but only cost a few dollars), I recommend the taxi service Modry Andel. You can book a taxi via their website and have a taxi driver waiting for you when you get off the plane with a sign and everything. If you book it in advance, you won't even have to give him the address, he will know where you are going from the website. They also have different discounts and you can request an English speaking driver. I just took a taxi from the airport this weekend and it cost 345czk (roughly $17US).