In a word, or rather 2 words - private transfer.
I found bus horrendous. Had to take a shuttle bus from terminal 1 to terminal 2 to pick up VEA and it was such a sea of people. No queue, no system, just pushing, shoving (some nationalities worse than others) and rude drivers. Very stressful.
Have no experience of the train but I believe it's very good, especially if you land in the same terminal as train leaves from.
We (DD & I) took private transfer last time and it cost me double what the bus cost on my previous trip but it was worth every single penny. We were checking into our hotel within hour and a bit after landing. Driver met us and we walked 10m to the door and car was right there, complete with choice of DVDs for my DD.
On previous trip, we hadn't even left the airport 1 1/2 hours after landing.
I'd check out costs. Private transfer is around 60 euro each way. I used Inter Shuttle Prestige & have booked them for my next trip also.
Enjoy your trip when you go.