Generic answer as you haven't mentioned any specific areas or issues you've had in the past. Generally the performance is a lot better and it's more stable. There are also more capabilities in the page designer and a new navigator designer has been introduced. 

At this point (depending on how urgent the upgrade is/your specific constraints) I'd probably evaluate whether to take Upd7 or wait for Upd8 which is being released 30th of April.

It is rather an urgent update … UPD 7 fixes a bug with parallel currency and posting vouchers.

Then I'd definitely go for it. Are you using Aurena? Performance in Aurena is a lot better in Upd7. 

Please make sure if you have projections in your permission sets that you test them properly. Since a lot of functionality has been put in these updates it is good to schedule proper testing time. And test the PO authorization, there is an information message all of the sudden popping up, not a blocking issue and there is a fix but something to have tested. The remainder of the testing went quite smoothly.

Currently working at a customer updating from 4 to 7.