echo hello works for no spaces scenario, but it is not a good practice.

echo "hello" allow you to expand variables. For example:

V="Hello Guy!"

echo "MyVar: ${V}"

it produces:

MyVar: Hello Guy!

Instead, echo 'hello does not expand variables. For example, the latter example produces:

MyVar: ${V}

Thanks to someone, the solution is simple.

Remove those double quotes and escape the !:

echo Hello\!World

or with bash 4.3 or newer, use double quotes but make sure the ! is immediately followed by the closing quote:

echo "Hello!""World"

From the release notes in bash 4.3:

l. The history expansion character (!) does not cause history expansion when followed by the closing quote in a double-quoted string.

Best is to use single quotes inside which all characters lose their special meaning¹.

echo 'Hello!World'

Or disable csh-style history expansion altogether with:

histchars=

Or:

set +o histexpand

Or:

set +H

Note that history expansion is only enabled by default when bash is interactive, not in scripts.

^{As long as the deprecated `...` form of command substitution is not also used, as inside it, \ retains a special meaning even inside single quotes.}