ooze shield vs priming tower, do you need both? I've been experimenting with two color prints. In my first test, I enabled a priming tower and the print came out OK, but there was definitely some oozing from the non-active head and left a lot of blemishes on the print.

I'm trying another print now and I also enabled an ooze shield.

This got me to thinking, if you are going to print an ooze shield, do you need a priming tower?

I'm using a lulzbot Taz6 with the dual extruder v3
I have the same printer you do.  I recall that the ooze shield is printed in alternating layers; first from E0 and then the next layer from E1.  But on a given layer, I don't think that there is a guarantee that the ooze shield will be printed in the filament about to be laid down for the part of the layer.  (But I might be wrong on this.)  But when it comes time to print the ooze shield, what will happen if the filament has already drizzled out during the print of the last layer?  The first part of that ooze shield won't get printed properly and might end up causing a print failure.  

As a separate issue, I found that an ooze shield is only helpful if the overall XY diameter of the print is not too great.  This is because it only helps when the print head crosses the perimeter.  If the print head spends a fair amount of time inside the perimeter, then the idle head can still continue to ooze out unwanted filament.  

So for many of my prints, I started using the priming tower, but skipping the ooze shield.