A good speed of internet will vary from person to person and what you do on the internet.
For watching youtube or streaming other content such as Hulu, Netflix etc then 3 Mbps is usually sufficient enough for a few users.
For others who download or upload a lot of data then having a high speed FIOS internet connection of 100 Mbps up and 100 Mbps down would be needed.
It entirely depends on your use as to what speed works best for you.
I have 3 Mbps down and 2 Mbps up DSL internet and it's more than sufficient for what I do on the internet.