User blog comment:Tinyvillageplayer/Dino Collecting/@comment-5200570-20130528032136

This completely depends on which dinos they have and how attatched to them you are. Some dinos have become quite difficult to obtain so I wouldn't suggest fusing any of those if you don't have duplicates. So if you're just looking to free up room then it would be best to start fusing your tier 0 dinos as they are the easiest to get again and then eventually you'll start building up duplicates of tier 1 and 2 dinos to fuse working your way up the ladder.

However, some people are partial to the first born dino in their village of any or all species. Myself, I still have the first hatched of every single dino I've gotten and many have already had their first birthday. But if you don't really care about this and are only worried about dino capacity, fuse your lowest tier dinos, except rare tier 1's, to clear up space and hopefully get something new.