I currently use a Signalink USB TNC and a AEA DSP-2232 TNC for digital operations.
My favorite digital mode on HF is packet radio and also FT8. Also, I like to run the older digital modes such as RTTY, Pactor 1, and AMTOR. Recently I have been experimenting with FreeDV, VARAC, VARA HF Chat, Freedata, SSTV and QRSS.
https://www.youtube.com/watch?v=ijvDIEt5eVQ&t=982s
https://www.sigidwiki.com/wiki/Category:Amateur_Radio
https://ares-mo.org/wp-content/uploads/2021/03/Missouri-Section-ARES-Digital-Data-Guide-2.pdf
Getting started with digital communications
https://pe4bas.blogspot.com/2020/10/operating-mode-comparisation-chart.html
https://w7jcr.files.wordpress.com/2016/03/digital-messaging.pdf
https://www.youtube.com/watch?v=tXLXe9C7JX8 (History of amateur radio digital modes)
https://www.qsl.net/zl1bpu/DOCS/70%20Years%20of%20Amateur%20Digital%20Modes.pdf
https://www.pa3fwm.nl/technotes/tn09b.html
https://vu2nsb.com/digital-modes-ft8-below-noise/
https://kf6hi.net/radio/SNR.html
https://tapr.org/pdf/DCC2018-KC5RUO-TheReal-FT8-JT65-JT9=SNR.pdf
https://www.qsl.net/sv1grb/psk31.htm
https://www.pa8s.nl/knowledge-base/frequencies-for-digital-modes/
HF digital communications software:
https://physics.princeton.edu/pulsar/k1jt/
http://f6cte.free.fr/index_anglais.htm