The short version
If TuxGuitar already does what you need, keep using it: it's free, it opens Guitar Pro files, it shows tab and notation together and it runs almost everywhere, including Android. guitarnotation is for when you want MusicXML import, a fretboard with chord shapes behind the notes, and exports that take your songs back to Guitar Pro and to notation programs.
Price
TuxGuitar is free and open source. guitarnotation costs $25 once, with every feature included and no subscription.
Files
Both open Guitar Pro files from .gp3 to .gp, and MIDI. TuxGuitar exports MusicXML but doesn't open it; guitarnotation opens MusicXML, including compressed .mxl, so scores from MuseScore, Finale, Sibelius or Dorico come in with their strings and frets when the file has a tab staff. guitarnotation also exports .gp files for Guitar Pro 7 and 8. See MusicXML to guitar tab.
Reading and practising
Both show tab and standard notation, a fretboard during playback, and slow down and loop. On guitarnotation's fretboard the current chord's shape stays faintly behind the note you're playing, and the chord diagram you're on is highlighted at the top of the score, so you see where the melody sits in the chord.
Writing tab
Both are built around typing fret numbers from the keyboard. guitarnotation keeps tab and notation aligned beat for beat as you type, so you read the rhythm on the staff while you enter the frets, and Alt+Up and Alt+Down move a note to the next string at the same pitch.
Platforms
TuxGuitar runs on Linux, Windows, macOS and Android. guitarnotation runs on Linux, Windows and macOS, with one licence for all your own computers.
Try guitarnotation's player and editor free in your browser, or see all the Guitar Pro alternatives.