Both the WeMOS D1 mini and the WeMOS Arduino copies that I got were hugely problematic. Basically their USB/serial ports were rubbish and I ended up have to program them like bare boards. So make sure you get genuine WeMOS if that's what you want, even if they cost a bit more.
ESP-01s with a separate USB plug-in programmer are OK, but they are very limited for experimenting (only two pins). They are great for small space applications, but that's it.
The DEVKIT 0.9 board is very good. A bit dated and clumsy on a breadboard, but stupid cheap and it works very well. You might want to get the v1.0 if you want to try it out the latest capabilities, it's not that much more expensive, and it's neater on a breadboard.
I have also tried a "Witty". It's like a DEVKIT 1.0 but with a separable base. That works very well for me, I use the base to program standalone ESP-07s and ESP-012s and it works perfectly. Might be OK for a beginner, as it has a built-in experimental 3-channel LED and light detector. I have a review of it on here somewhere, it was the second board I got.
Personally, if I was getting something for a beginner experimenter, I'd get either the WeMOS "D1 mini" or the DEVKIT 1.0. Just plug in USB and play.