So many times have I lost games early on as a Terran because whenever I sent my army to attack and I had a Raven or a Ghost, the hotkey would select the Raven or Ghost before my Marines/Marauders, I still mess up with that till this day, get my army wiped out, I think it would be a really good change and a simple one if they gave us the option of customizing what units to prioritize in order of relevance(to each player) instead of just tabbing between units or put them in seperate hotkeys, some players like me just cant quite learn how to do that because pressing your hotkeys and having Marines with stim ready has always been the norm for all Terran players, I’m sure the other two races have the same concern, and it would make the learning curve just a bit better
Control+shift click marine marauder before fight and assign to group /just Tab and dont mess up
Learn to use Ravens on a separate hotkey, have them move-command on a unit to follow them then use their hotkey when you use them. You can also use Tab to cycle through units clockwise then use Shift+Tab to cycle through counter-clockwise.
I want my Thors to prioritize Overlords and Observers like it used to. 
I made a suggestion a while ago to have the useless middle black bar of the UI serve as a spellbar with all your race’s spell available here, all displayed at once.
This has been asked from the community a lot of times but Blizzard never incremented it. Terran players suffer about this especially because you want stim ready to use but the only way is to assign spellcasters to another group.