I don't think someone who's using an Arduino will want to go to the bare MCU directly, and WeMos is the best breakout, so why recommend anything else?
I generally find it better to recommend one thing to new people than to inundate them with options that they can't differentiate between and that, ultimately, won't matter to them. If you don't know what you want to get, what service am I doing you by showing you many different options that are more or less the same, and which you don't know enough to choose between?
http://frightanic.com/iot/comparison-of-esp8266-nodemcu-deve...
wemos has a smaller form factor, but lacks breakout, has the ch34 and is headless so maybe not suitable for beginners like i think of the nodemcu.
edit: also I'd like to add that the nodemcu and sparkfun thing already have a esp32 upgrade available where the wemos has not.
But hey, just my opinion.
You'll want one of the boards listed on this webpage: http://esp32.net
$3 or $15 really doesn't matter here.