If you happen to be using the "D&D 5th Edition by Roll20" character sheet, I would use the Attack template. First, go to your character sheet configuration tab (the gear icon just below the XP field). In the upper right region of that tab, set Roll Queries to "Query Advantage" and Auto Damage Roll to "Auto Roll Damage & Crit". Select the appropriate token and run a macro similar to the following:
@{selected|wtype}&{template:atkdmg} {{mod=+[[@{selected|charisma_mod} + @{selected|pb}]]}} {{rname=Eldritch Blast}} {{r1=[[@{selected|d20}cs>20 + @{selected|charisma_mod}[CHA] + @{selected|pb}[PROF]]]}} @{selected|rtype}cs>20 + @{selected|charisma_mod}[CHA] + @{selected|pb}[PROF]]]}} {{attack=1}} {{range=120 feet}} {{damage=1}} {{dmg1flag=1}} {{dmg1=[[1d10]]}} {{dmg1type=Force}} 0 {{crit1=[[1d10[CRIT]]]}} {{desc=Some Description}}
Here is an example output when selecting "Advantage" when the macro runs, rolling a crit on the first roll (for 9 extra damage). Note the second roll is greyed out. If it had been Disadvantage, the 22 would have been greyed out and no crit damage would roll.
EDIT #1-- If you set to "Always roll Advantage" instead, then both rolls would remain in bold coloring and you would just decide which to use by looking at it. This is what we do in our games, because it is less clicking. Note that if the roll was not actually with advantage but the second roll crits, then crit damage would still show up in the damage field. You would simply ignore the crit damage in that case. Mousing over the numbers in the chat results tells you where each number comes from.
Edit #2 -- you can still add the emote flavor text prior to calling the roll template, or put it in the description field.

More info on how to use templates for this character sheet can be found here.
https://wiki.roll20.net/D%26D_5e_by_Roll20_Roll_Templates