I cannot find exact network performance details for different EC2 instance types on Amazon. Instead, they are only saying:
FWIW CloudFront supports streaming as well. Might be better than plain streaming from instances.
Almost everything in EC2 is multi-tenant. What the network performance indicates is what priority you will have compared with other instances sharing the same infrastructure.
If you need a guaranteed level of bandwidth, then EC2 will likely not work well for you.
For t2/m3/c3/c4/r3/i2/d2 instances:
m1 small, medium, and large instances tend to perform higher than expected. c1.medium is another freak, at 800 MBit/s.
I gathered this by combing dozens of sources doing benchmarks (primarily using iPerf & TCP connections). Credit to CloudHarmony & flux7 in particular for many of the benchmarks (note that those two links go to google searches showing the numerous individual benchmarks).
The large instance size has the most variation reported:
Burstable (T2) instances appear to exhibit burstable networking performance too:
The CloudHarmony iperf benchmarks show initial transfers start at 1 GBit/s and then gradually drop to the sustained levels above after a few minutes. PDF links to reports below:
t2.small (PDF)
Note that these are within the same region - if you're transferring across regions, real performance may be much slower. Even for the larger instances, I'm seeing numbers of a few hundred MBit/s.