A nicer looking book

if you take care with your conversion choices.
PDF is a very poor format choice when it comes to reflowing to fit a different display than the document was
designed for.
plain TXT has little style capability.
The rest have some style

. How well your device handles that (and still allow Reflow and Resize) is up to you to judge.
For me. EPUB was the choice.
The first thing I do to make a pleasing 'read' on my PEz (5" display), is set the
body base font to 1.2em and the margins to L=2pt,R=16pt
This allows me to read with a mid point Zoom setting (text about the same size as the paperback) and avoid text smearing on the @#$% ADE page numbers on the R-edge.