The approach of network traffic obfuscation is quite similar in both projects, however there are some major differences.
TOR is used by a vast majority of users as a proxy service for the clearnet, what we commonly call "internet" but only a small percentage of users are acting as nodes actually relaying traffic for others.
I2P on which Kovri is based has a different approach and is not designed to proxy clearnet traffic but to build a really decentralised network of equal nodes which all act as relays by default.
In general, TOR is more centralised, since comparatively few strong nodes with good connectivity are relaying most of the traffic. This is even more valid for "exit" nodes to the internet, since many relays don't want to act as such for security or legal reasons. An attacker might setup many of these strong nodes to control a major chunk of all relayed traffic and log its activity on the network to determine where it actually comes from and where it goes to.
These aspects disappear for I2P network since there are no "exit" nodes and for any node it is not distinguishable if the current traffic it relays (which is encrypted) is intended for the node it is actually communicating or if it is just another relay. Every single user / node makes the network stronger against attacks aiming to overtake the network and log its traffic.