Hasklig initially felt like the right font for me. It's based on Source Code Pro, which I like, although it's never been my favourite programming font. It's very round, and a bit wider than I normally choose, but legible, and the ligatures look nice.
However, I do like the idea of having a ligature for "!=", and Hasklig limited ligature set doesn't include one for this.
Fira Code looks a reasonable amount like Hasklig, really. It's a little narrower, a little less round. I found it very slightly less legible at first, but it was a close second place. Notice that it does include a not-equals ligature:
Although I started with Hasklig, I have since switched to Fira.
Monoid is big. It's the only one that I'm showing here in 12pt instead of 13pt, and even that feels bigger than the others. It's pretty legible, but the weight feels a little too light as a result to me. Feels like coding in Helvetica Neue Ultra-Light.
Pragmata Pro is narrow and tall. The wideness of Source Code Pro is one of the reasons I stayed away from it at first, but Pragmata feels almost cramped to me. I like the idea of firing a lot of text in, but it feels less legible as a result of its narrowness, so I'm not sold.
If I felt this were the right font for me, I suppose I would probably purchase it anyway, but at that price I'd want to be sold right away, and I'm not. If it were cheap, maybe I would have impulse-purchased and given it a longer trial.
Pragmata does have a lot of nice features, so if you do feel so inclined, it's still worth looking at.
To be honest, these are all pretty decent fonts, and if you're interested in having programming ligatures, I urge you to try some of them out and see which one fits for you.
For me, I think I'm going to try Fira Code for a while. If Hasklig or Source Code Pro adds more ligatures, I might consider going back. I'll also be watching for other ligature programming fonts (Inconsolata, for instance?).
Have any suggestions I should try?