My answer is usually "depends"!
There are a lot of top coat options out there, even though mainstream gourmet paints have led us to believe wax is the only way to go. Having used wax quite a bit, and then experimenting with a variety of other "tried and true" methods, I have all but ditched the wax.
With the huge onslaught of gourmet chalk/milk/mineral paints on the market now, I feel like it has created a culture of DIYers that have only been given one side of the coin in terms of information on how paint works and what options are available to them. When I was searching for reliable information, I always lean towards the old school woodworkers, the ones that don't have any affiliation with any brand or product, and people that will just tell you what WORKS.
Here is a quick breakdown of the most common top coats that I have used:
*All of these are available at local hardware stores*
It also MELTS and feels waxy to the touch on a lot of pieces.
I have used some gourmet waxes, which do seem to smooth out a little bit better, but still a longer process.
Wax does also slightly yellow light coloured surfaces.
Goes on milky, dries clear - no yellowing. Perfect for white surfaces, or a colour that you don't want to "deepen" with poly etc.
Can appear much more "plastic" than the oil finishes, but does provide a good protective layer. Does potentially react to high heat (aka coffee cups or hot pans), so not the best for high traffic table surfaces.
I use this often as it is the only real choice for bright whites (to keep them from yellowing).
Minwax Tung Oil
A wipe on oil finish that tends to not yellow, so can be used on white surfaces. The downfall to the tung oil is that it doesn't form a protective later like the Varathane or poly, but rather soaks in to the surface. Gives a beautiful sheen to stained wood or painted pieces, but not ideal for high traffic surfaces.
Wipe on Polyerethane
This is hands-down my favourite top coat to date. It is super easy to apply (just need gloves and a lint free cloth!) and gives the most beautiful finish of all of the other top coats. It is also the strongest finish of the 4 (however, wipe on poly does need more coats than brush on poly because the wipe on is diluted).
It DOES yellow lighter surfaces, so this cannot be used on whites on other bright colours that you want to keep their vibrancy. A very beautiful hand rubbed finish though - no streaking.
Does have a longer drying time, and can take 30-60 days to fully cure.
There are a lot of options for top coat out there. If you talk to a wood worker, or other person who has been in the trade for a long time, most will tell you that polyurethane is the way to go because it is the most durable and visually appealing finish. The smell is not for the faint of heart, but the finished product is so worth it!
Tung oil would me my next top choice, followed by Varathane and lastly the wax.
And just remember - companies that survive on you buying their $35 wax aren't going to tell you any different, so do your research!
Thanks for reading :)