In a real "emergency" - that is, down 2qt+ - then add any viscosity, either dino or synthetic to top off to the fill mark.
Then, if you have mixed viscosities and/or conventional/blend/full synthetic, then have a full oil plus filter changed as soon as practical. Seen this advice in various locations, including the "official" MoCo recommendation in the owners' manual.
If you are mixing brands, and the weights are the same & you're either all dino, all blend, or all synth, then (IMO) you can wait til your next scheduled service to change. As Don mentioned above, there are synth blends, but since those are formulated by chemical engineers (at least I would hope so) then I wouldn't personally leave dino + synth even of the same viscosity in if I could get a full oil & filter change done very soon.
Then the last thing to ask is, if you've had a 2qt+ low situation - how did it happen? Bad valves or rings? Straight leak? Forgot to check often enough?
PS I generally don't top up to the full mark - the 110 motors I've had don't seem to like the last quarter of a quart, so I don't add until I need a half quart according to the mark, then I'll add an eyeballed pint. If I go a little over, it pukes it out anyway through the AC.
On dino vs synth, I'm a full believer in synthetic (non-blend) for best service - both hard duty (ie, the heat our motors generate) and mileages. I don't think a few bucks saved is worth it, and just look at the difference at 5K miles between how dino looks to the eye versus synth - filthy versus clean.
If you've had a lot of parade duty high heat, or high speed/high heat conditions, change it sooner. If you're in a cool climate and most of your rides are 50mph backroads with few idling conditions, change it a little later.
But put whatever's at hand in it if you're not hitting the dipstick when you check it & then find out why it happened when you service it.