The best free and most up to date phylogenetic tree on the internet?
Available ressources

I would recommend oneZoom.org is probably the best ressource. oneZoom.org is based on openTreeOfLife.org (for phylogenetic relationships) and eol.org (Encyclopedia Of Life) (mainly for the pictures I think). If you do not fancy to much the display and links of oneZoom/org, then I would just recommend openTreeOfLife.org.

There is also tolweb.org but it is not as nicely updated as openTreeOfLife.org (and therefore openTreeOfLife.org) and the dates are harder to find.

Particularities of oneZoom.org

I particularly like that for each node oneZoom.org offers links to


wikipedia
encyclopedia of life
the red list
NCBI


, which makes it a very appreciable tool. oneZoom.org has the advantage of a nice display (although a bit slow to load IMO) and is easy to navigate and get time to the Most Recent Common Ancestor of a lineage.

I also like that you can just add the species name after "#" in the URL and it will jump to its node. Here is the Kagu for example.

Potential issues in oneZoom.org

Of course, oneZoom.org contain a few mistakes! Some of them are unintentional (wrong picture, misrepresentation of what is known from the literature, fail to update information), some of them are caused by lack of knowledge of true phylogenetic relationships. oneZoom.org does not say how certain we are that a given speciation event is correct or correctly dated, it just display the best estimates we have. If a specific node is of interest to you, you will need to go to the scientific literature which will give you much more information about what we know and what we roughly guess.