Scott 405 or 406 are perfect for single line, 300 is perfect for double line. When you want to test yourself on something difficult, pick up 3 or 4 Scott 416's, and discover how tough it is to find a watermark on a yellow stamp.
Zippo owns the Ronsonol brand and they are universally the same product now. But beware at the dollar store, believe it or not there is knockoff / fake Zippo lighter fluid. It contains higher fractions that can leave an oil stain on your stamps.