I was in a similar situation a few months back and went with new Assioma Uno's.
If you're just looking to add power numbers and structured training, one sided power is fine. Regarding choosing between the two, I've had zero issues with the Assiomas and is why I chose them. The reviews noted that they just plain work without complaint. The battery on the Assiomas last a really long time; I charge it every few weeks and I ride 6 days a week. The Vectors had a lot of reviews noting issues with the batteries and the covers that would cause a lot of the problems. DC Rainmaker and GPLama noted these issues and gave a mixed review IIRC which is why I didn't go with the Garmins. For the amount of money I was about to spend, I didn't want a product that was finicky all because of a battery cover.