Google Keyword Planner vs. SEM Rush

What would you consider to be the most accurate keyword research tool when it comes to keyword volume?

I've been using the Google Keyword Planner to get a rough idea on the volume of keywords, but some of
the other keyword research tools come up with keyword volumes that aren't even close to the planner.

For example, a keyword in GKP shows a volume of 14,800 while SEM Rush shows a volume of 50. There
are a number of keywords that come up that way when I'm searching. Another one shows 18,100 in GKP
but it only shows 1,800 in SEM Rush. Why is their such a dramatic difference in volume between the two?

Wouldn't you expect the tool by Google to be the most accurate?

Let SEMRush explain it themselves:

http://www.semrush.com/blog/publica...mes-in-semrush-different-than-google-adwords/

Google's tool would give you accurate results, semrush and others do not have their own way of figuring volumes out, they all depend upon Google.

Okay, I've figured out my problem. The SEM Rush volumes are showing US only,
while the Google volumes are showing the global reach for the keyword unless
otherwise specified. So, obviously these keywords aren't too popular in the US.

I prefer Google Keyword Planner as most useful tool. The data comes directly from Google so it should be the most accurate. It's also the main indicator for their adwords campaigns and I guess they won't risk it to send false info to their clients.

Well tools will never give you the exact result. Every single tool will show you a different result but you can consider Google keyword planner as Good tool for checking keyword volume.