The different responses above so perfectly illustrate the dilemma! The ARL camp is the majority, but there are some votes for taxi as well....

I focused my question on traffic at that time of day, but I guess the other variable here is after a 34 hour journey, do I want to put up with the crowds of ARL & MRT? Google maps says the trip from the airport to my hotel by car is 30 minutes to 1 hour. I'm guessing by train is about 35 to 40 minutes based on the all the videos I've watched (getting tickets, ARL to Makkasan, and then MRT to Sukhumvit - all the walking, waiting the couple of minutes for trains, etc.)...

The long walks would be great after that journey... but let's say that traffic is moderate and it takes 45 minutes by car... now it's a push basically and it's trading cost for comfort: e.g. ~$15USD more to sit in the back of a taxi instead of dealing with the crowds of the trains. I do travel light, so luggage isn't an issue (one standard carryon and a small backpack).

BTW - I really like mass transit when possible, I've ridden mass transit in every country I've visited (except Dubai & France) I've even used the BTS in Thailand on a previous visits.

One thing I haven't seen anywhere is whether there is generally a queue for taxis? That could add some time to the mix...