Most definitely a Chromecast is the simplest, one of the cheapest ($35), and very effective.
With a Chromecast you can buy any TV that has an HDMI port (so you needn’t buy a more expensive “smart TV” and have to debate which brand to buy). What’s also great is that it works with apps that guests are probably already familiar with (e.g. YouTube, Netflix), and across iOS and Android. Finally, for those unfamiliar, a URL to the instructions on how to use one is displayed on the TV screen (www.chromecast.com/learn). The only downside is that it requires a constant internet connection, but that shouldn’t be a problem for most hosts.
I bought one for my father, who is in his 60s, and he got it up and running and was casting videos from his iPad to the TV very quickly. There are even games that can be played on Chromecast (e.g. Monopoly Dash, Scrabble, Cards Against Humanity). You use your phones to control and interact with the game on the screen, and again some of these work across Android and iOS.