Always remember to ( Ctrl/Cmd + G ) your text and your custom underline shapes together once you are happy with the alignment. This prevents your beautiful typography from falling apart if you move the text box later!
If you're looking for more creative control or a specific effect, you could use a Brush to create underlines. illustrator underline text
The default underline is rarely visually pleasing. It usually sits too close to the descenders of letters like y, g, p, and q , and the stroke weight is often too heavy for thin fonts or too light for bold fonts. It works for wireframes, but not for final designs. Always remember to ( Ctrl/Cmd + G )