This question is similar to this one and this one but it is sharply focused on the contemporary English language and on font design. When you are designing and "stress-testing" a font, you need to see all of the letters and digraphs, and any ligatures that you may be testing, and if any letter has more than one glyph then you need to see all of them too – and you need to see all of this in a realistic looking text. "Lorem ipsum" simply is not the tool for this. It does not show the letters "k", "w", "y", or "z" at all – so it is totally useless if you want to see how the unusual-looking descender on your "y" fares in practice when it precedes say an "i" or an "l", when it follows a doubled consonant that you'd forgot that "y" occasionally does follow, or indeed when it does anything else. Does the rightmost slanting line of your capital "W" look all right before the letter "r"? Don't ask "Lorem ipsum"! "We thought you were woozy, but he knew you were crazy" may be a sentence that makes some of your design choices look absolutely ridiculous, but don't expect Cicero to give you forewarning when somebody wants to use that sentence in a poem and they email you to tell you your font doesn't cut the mustard.
I realise the worldwide web has numerous texts in English, some of them lengthy, and that it's easy to find one :-) Also there are various humorous alternatives to "Lorem ipsum" out there as alternative placeholders. But my question is this: what is a good text to use when designing and testing a new font for the English language?