One of my top five chemical reactions is the thermite reaction.Sometimes it is difficult to demonstrate it due to lack of space or safety concern. Here is a neat way to show the redox reaction in action:
I can't say that the video you showed of the instant thermite is my favorite but I did perform the traditional flower pot into a bucket of sand slow cooking thermite reaction for our annual physics and chemistry demonstration and I have to say it was the most exciting reaction I have done!
I have 2:
The Blue Bottle reaction - demonstrates a lot of principals at once, easy to follow, color changes always attract attention
30% Peroxide in large plastic soft drink bottle + KI -> "Elephant Toothpaste" without the detergent. Neat to see the bottle shrink from the heat.
Watching the videos was frustrating so I only watched the 1st; too many interputions (plus the ad was annoying).
I love color, in art, chemistry, whatever so I guess the various clock reactions, especially the Orange and the Black Princeton Clock Reaction would rank quite high on my list of favorite reactions. However, I've never run one so my favorite reaction that I have run--many times--would be the Diels-Alder Reaction. The first was in Advanced Organic Lab as an undergraduate at the Univ. of Minnesota in 1960. This was followed by several preparations of 3-vinylindoles and subsequent Diels-Alder reactions with Prof. W. E. Noland at U of M. As a grad student with Prof. E. C. Taylor at Princeton, one of my projects involved DA reactions of aminodienes and dienediamines. Something about the deceptive apparent simplicity of the reaction, ordinarily not requiring catalysis, just mixing the reagents and watch it "zip up". Fascinating, even after sadly leaving the lab 40 years ago (but still a chemist--for life). Sorry--no videos.
My favorite is "Dichromate Volcano":
N2 + 4H2O + Cr2O3
It is very easy to set up for demonstration and students like when "something is burning". This is a great experiment to discuss the signs of a chemical reaction, introduce the concepts of decomposition, enthalpy and oxidation-reduction.
The screaming gummy bear (Haribo or generic gummy bear in molten potassium chlorate). I remember being very intrigued by the original discovery in J Chem Ed, and now there is a video!