There are many varied opinions on this subject...
Most of us use testmy.net, and for download speed tests use the 12MB file size and for upload speed test use the 5MB file size.
Small file sizes yield erroneous results because of the bandwidth management software used by WB/Exede which creates burst-speeds when their is less demand.
If you stick to the same test site with the same file sizes used for your tests and do those tests about the same time each day you can begin to judge how well your installation is performing.
Exede12, ViaSat-1, beam 342, Albuquerque Gateway, Denver AcceleNet servers