Help with Data Transfer

I have a Mac Pro (2008, 3.1) with three WD 3TB EHDs holding 6 years worth of Aperture Libraries, Vaults and also Time Machine.
I am upgrading my system to a 2013 27" iMac with Drobo 5D.
What is the best way to transfer data from the old external hard drives to the Drobo?
1] Connect the Drobo to the old Mac (has firewire) and transfer data WD -> Drobo. VS
2] Set up new iMac with Drobo and plug in WD HDs one at a time to iMac and transfer data.
Thanks

Either way will be fine (arguably it by be a little quicker on the new machine but there won't be much in it). Either way I'd use a sync tool to copy your data to the Drobo.

Can you explain sync tool and how it helps in this instance?

A sync tool, rather than doing just a copy does a copy and compare. It's handy A) to give you confidence that what's been copied is intact at the other end and B) means when you're doing large quantities you can stop and resume the process without needing to know where you had got up to.

A sync tool will compare files and or folders and ensure that the source and destination match, taking any necessary action the ensure that.

Have a look on the Mac App Store for Folder Sync

Thanks for that.
In theory once I copy my Aperture Libraries, the Vaults will not be as big an issue. They sort of "sync" themselves and I can always "refresh" them when the new system is up and running.