- TEST‼︎
U+203C DOUBLE EXCLAMATION MARK
U+FE0E VARIATION SELECTOR-15 (text variation selector) - TEST‼
U+203C DOUBLE EXCLAMATION MARK - TEST!!
U+0021 EXCLAMATION MARK
U+0021 EXCLAMATION MARK - TEST‼️
U+203C DOUBLE EXCLAMATION MARK
U+FE0F VARIATION SELECTOR-16 (emoji variation selector)
No reasons to use an emoji version (U+FE0F).
And I don’t like to use any invisible characters anyway, not text variation selector either (U+FE0E).
Then single double exclamation mark character or 2 regular exclamation mark characters… I would leave it up to case by case… 
U+203C is good IMO, I have used it in some MB stuff like 愛をとりもどせ‼ because on the covers it looks like a single character (diagonal twin exclamation mark).
Ah there it displays nicely, when in sentence.