How accurate are Keyword Planner search numbers?

Okay, so I have two keywords:

• Keyword #1 has 2900 exact match searches a month
• Keyword #2 has 6600 exact match searches a month

...or at least, according to Keyword Planner that's the case.

But according to Google Trends, Keyword #1 has (what seems to be) twice as many searches. Are the numbers in Keyword Planner that accurate? Should I go ahead and bother ranking Keyword #2?

Any help would be appreciated.

Planner is older data and averaged over 12 months, Trends is much more up to date.

The numbers you see in the Planner are also rounded into chunks - ever noticed just how many 6,600s there are for example?

Also worth creating a mock campaign in the Planner and seeing what that shows in terms of daily impressions. Probably something entirely different.