I’ve got the steel core plastic outer icetoolz ones.
If you can use the std puncture repair kit plastic ones without snapping them or bending them to uselessness, you can probably use your thumbs.
So really, if you need levers, you need need good ones. Icetoolz ones do the trick and are diddy enough for seatpacks.
I’m sure all of them ^ are perfectly good too! Although I found the park tools ones a bit thick, they introduce too much extra tension if you need to get a second one in.
edit: they’re exactly the same as these, bar the name in the middle.
http://www.halfords.com/cycling/tools-maintenance/tools/xlc-tyre-levers-with-steel-core-3-pieces