I want to go to Amsterdam this weekend. What are the possible modes of transportation available? I would like reach Amsterdam early morning so that my day remains intact. And similarly would like to leave Amsterdam late night on Sunday. What are the possible options?
Train traffic between the Benelux countries has been heavily screwed up recently due among others to the Fyra fiasco and the compatibility problems between Belgium and Luxembourg , ... Hence, at first sight the train does not look too sexy for your trip. However, that's probably the most viable option.
The Megabus and Eurolines schedules are not so interesting for you. That could be an option if you lived in central Brussels. The bus does not arrive in a very central location in Amsterdam. This implies extra costs and extra travel time. As compared to rail prices, the prices for the bus might look appealing at first sight. However, if you factor in the ticket from Leuven to Brussels and the local ticket in Amsterdam, the picture changes. These to additional legs have also to be added to the travel time, which is +- 4 hours for Brussels-Amsterdam.
From Leuven, I would definitely go by train, despite the up to three changes that are now involved (compared to one before). If you go by conventional trains, it takes 3h30 from Leuven to Amsterdam. The first train leaves around 5:30 AM and you will then be in Amsterdam Central Station around 9:00 AM. After that you have a connection every hour. The price for a return trip using conventional trains is 43.20 EUR during the weekend. This is a fixed price and don't have to book years in advance to get it. You can check schedules, prices and book the tickets via the SNCB Europe website. Tickets can also be bought at the station for the same price.
Just one word of caution. I would not leave Amsterdam by the very last available connection. Connection times are rather short, especially on Rotterdam. If there is a delay, you still have a joker if you are not on the last train.
A faster option is the Thalys highspeed train. That only involves one change of train in Antwerp. It takes all in all around 2h30 from Leuven to Amsterdam. However, it is much more expensive. If you check schedules via the SNCB Europe website, Thalys connections appear as well.
To be complete, you could consider hitchhikng or ridesharing. But it may be too hard to find a ride when you need it. They are more unpredictable and require some flexibility.