Is the best way to get to Brussels from Amsterdam by train. How often do they run. Reservations required?
The Thalys high-speed train. They use airline style pricing, so the sooner you book the cheaper it will be. Schedules and fares here:
Thalys runs just about hourly.
all seats on Thalys are by reservation only
We will be travelling from Amsterdam to Brussels in May 2014 and booked the Thalys 90 days in advance and got good fares (29 Euros one way for adult and 15 Euros one way for a 4 year old). I researched the site and saw that they posted their fares after midnight Belgium time 90 days in advance and so you can plan to be online the minute the date gets posted to snag the cheaper fares) There are other intercity trains that need no reservations but those require a transfer. Thalys is defintely faster if that is what you consider best. seat61 website (click on Belgium trains and Thalys) and the Thalys website itself was useful in our planning.