With an external keyboard selection works like on a pc, just hold shift and use the arrow keys.
The only thing that's really missing to make editing text on the ipad a breeze is a way to select while moving the cursor with the two finger gesture above.
I am a heavy mouse (and trackpad) user and have been for decades. Editing and refactoring code for me is all about the mouse. The same goes for editing prose, which I also write a significant quantity of.
The two-finger, on-glass "trackpad cursor" trick doesn't work well for me--it never has. It looks like the "ghost caret" is in the right place, but at least half the time, when I lift my fingers the cursor appears a character off in either direction. Verrry frustrating. Also, the two-finger trick requires the on screen keyboard and is clumsy to use if you are using an external keyboard.
About a year ago I gave up on my personal quest to use the iPad as a heavy writing device. It's just not for me. I picked up a bottom-of-the-line 12" Macbook and have never looked back.
It's a very interesting and surprising statement to me. For me the mouse is absolutely nowhere near convince of selecting text with keyboard. When your editor allows you to jump between paragraphs, words, ending and beginning of line (so pretty much every editor) it seems to be relatively easy to rapidly jump to place that one wants to select with couple of key strokes.
Keyboarding, mousing, editing is a very personal thing to folks who have to work at their computer all day. Lot's of different ways to work, lots of approaches to the work. Each person has to find their comfort zone.
You can. Double-tap a word or character so it's selected, then do the two-finger select gesture on the keyboard.
You don't need to double tap on the actual text or characters, you just tap-then-drag with two fingers on the software keyboard.