google tool and market samurai showing wildly different est traffic figures, Who to believe?

[Sonny Am]

Hi Warriors.

I am really hoping one of you can help me

I found a good keyword I wanted to build a site on. The cpc is a decent amount, and I have checked the top ten competition and it seems beatable however this is where the problem starts

Google keyword tool is showing est exact match traffic of 27,000 (local) where as market samurai is showing est exact match traffic at 13,902.

I would have assumed that google would be more trustworthy because its the actual root and the source of the information, but that may just be wishful thinking, another thing is that market samurai does not specify whether their estimate is local or global.

Can someone please tell me why they are showing dramatically different estimates.?

Also is there a tool or service I can use that will give me more accurate est traffic information.

Thanks ever so much in advance.

Sonny.