Currently on 11.2.6 , should i upgrade to 11.3 or stay ?
I would personally stay on 11.2.6. The chances of a jailbrake are higher than 11.3. You can always save your blobs for 11.3, while it's still being signed, in case it becomes possible to upgrade/downgrade to it at a later date.
iPhone 6 - 9.0.2 jb
iPad mini 4 - 9.0.2 jb
Apple TV 4 - 10.2.2 jb
iPad Pro 10.5 - 11.3.1 jb
iPhone 8 - 11.3.1 jb