Hi man,
I don't know for what do you want to use the internet connection, but:

1- If you want it only for browsing then get the [512KB] it is more than enough for browsing.
2- If you want it for browsing and watching online videos, download some stuff from here and there get the [1MB].
3- If you are using the torrents to download movies, music and can't live your day if you did not download something, then get the [2MB].

The speed difference can be noticed when you start downloading from a static IP or a direct download. The range goes like:
1- [512KB] up to 80 if you were lucky, most of the time between 60 and 70]
2- [1MB] up to 120 but most of the time the range is from 90 - 110.
3- [2MB] up to 200 but most of the time the range is from 140 - 180.

You should notice the download speed varies according also to the upload speed [especially torrent files], if you start for example downloading 3 torrents in the same file and one of them was having an upload rate of your maximum connection speed that can support. You will find that the other 2 would not even start because you reached the maximum upload speed. Try stopping that one that it is taking most of your bandwidth to upload and you will see the others go fast. It is irrelevant to the speed in most of the cases [download speed of the torrent], but it would be obviously depending on your connection speed as everyone got it's own support for the Max. download and upload speed. What I mean is a bad torrent [depends on trackers, leechers and seeders] would always be a bad one, no matter what connection do you have.

Best Regards