I've used TaxAct for years, but switched to a competitor to protest their price jump ($22 to $30). I've realized switching away from TaxAct was a mistake, as I like it much better over HR Block (paid $36 with 20% discount). Having bought both versions this year, I can compare them...
If you look at the display of tax forms, HR Block forms look low-res compared to near-PDF quality forms with your data filled in. It's much easier to read, in my opinion, in TaxAct.
HR Block has you enter each stock sale in an interview style, while TaxAct has a "Stock Assistant" that allows spreadsheet style entry.
There isn't much of a price difference between the two, but HR Block has a special refund offer (each $100 of refund can get you $110 gift card).
A couple times in HR Block I was presented with "please fill out form X and enter data here". But isn't that why I'm buying tax software, instead of doing it myself?