I have DM780 but I personally don't love HRD interface that much as it generates lots of overhead. It does have a multiple stream decoder which can be impressive.
A lot of people love FLDIGI. ...because it's free and it is the most tightly integrated into Flex. Probably a very good place to start to see if you enjoy digital
Then there is WSJT-X which is JT65 and JT9. Personally these modes are a heck of a lot more fun than PSK because you can easily work 100+ countries in a few days and there is always DX on no matter how poor the conditions seem on lesser robust modes such as CW or PSK.
I recommend that you check-out Fldigi. I have also used DM780 which is part of the HRD (Ham Radio Deluxe) package. Fldigi is free, but the latest version of HRD comes with a price. Older versions of HRD are still available at no charge and work fine.
You may also want to check-out the digital modes JT65 and JT9 which do not provide for "rag chewing", but are much more effective than PSK31 in terms of making solid, weak-signal contacts. The software you should consider for these modes is WSJT-X which is free.
I am using HRD current version.
What I like about HRD is that it is all inclusive; no need to got out to a website to download add on software.
I have used MixW and I tried FLDIG and they have not measure up to HRD; once you set it up.
They all have a quirky setup, but once you master that particular program: Satisfaction will be on site.
Since I use HRD for all my logging, it just makes sense to use DM780. The multi decoder is one of my favorite features and is implemented really quite well. That and the spotting integration just make it a great choice for me. YMMV! :D