I may write up a comparison if I find the time.
I'll wait until 1.2 (which seems possibly to be not ages away) before a more comprehensive review that compares the two. Makes more sense, as with 1.2 more features will be added and some topics will be fixed, so a review before that would be outdated quickly.
What I can say already is that I like the Events Manager and 1.1.5 works well enough already that I took it productive on my forum (albeit on small scale with only few events, only a subset of what I have planned). 1.1.5 does have a number of glitches that hinder full usage in the way I intended it (i.e. giving permissions to users in the way I'd prefer to create events themselves) but that's fair: It is a brand new software that was released less than a month ago, so glitches are absolutely to be expected and one would be silly to expect it to feature complete.
@Veer has proven to be
very responsive and quick, in fixing bugs as well as in implementing feature suggestions or feedback to existing features - so absolutely nothing to complain about. So I am looking forward for 1.2.0 which will probably be a huge step in features - but by that has through the implementation of huge and complex features as the calendar also so the potential for new bugs or to leave the track I'd like for the software in terms of UX, functionality or aesthetics (at least
in theory). We will see. And I already know that not all my wishes will come true in 1.2.0.
Calendar on the other hand is relatively mature - it is a well thought addon that offers good solutions for topics where Events Manager 1.1.5 is blank (but will no longer be blank in 1.2.0 in many of these areas). On the other hand Calendar does have it's issues as well - unfixed bugs, issues with certain recurring events and other things - not too many, but they have not been fixed for years, not even the easiest ones and the lack of developing the product further or generally attention of the developer for the product is not convincing. The latest version was released more than two years ago. Other than that it seems pretty robust - just that there are some concepts in it that I personally dislike (like i.e. the way it deals with a pictures) and where I clearly prefer the way Events Manager works. Possibly one could work around many of these with customizing, custom style and custom development but that's not my cup of tea and I do not want to open this can of worms.

And it seems to be stuck at the current state of development, so it is rather "take it as it is or shut up". Whereas with Events Manager I can to a degree take influence where it is going - a huge advantage.
So of the two I went for Events Manager after comparing despite it being - for obvious reasons - currently less mature and less feature complete. But I have the hope that this will change soon and even more over time and I value the attitude of
@Veer very much. On the other hand longterm we are talking about a marathon, not a sprint and only time can tell wether this persists longterm. It's often been seen that new products see fast releases in the beginning and some time later movitation stops as does development (as it seems to have happend with Calendar and many other addons). Not calling Cassandra and no signs for that (rather the opposite), but impossible to tell now. We will see.