I've been having issues with this myself, so I set up a simple test. I put the commonly used fonts with common error letters into Word, took a screen shot and set it as a sample image, and then ran it through different OCR activities in Quick Fields. Speed and balanced were terrible in all tests, so all OCR was set to Accuracy.

O 0 o I l L 1 B 8 4 9 s S 5 z Z 2 - Original Text Used for tests

I tested a number of the most popular fonts like Tahoma, Arial, Comic Sans, Verdana, Book Antiqua, Courier, etc... And also tested at 11 point and 14 point, and found a more obscure font called Consolas that has a slash through the zero, to see if that would improve results.

If you know you're scanning for numbers or letters you can set the advanced properties for the Zone OCR to favor numbers or letters, so I did Zone OCR with no bias, bias for letters, and bias for numbers.

Nothing read with 100% accuracy. ALL of the fonts had fails, with zero and capital O being the worst at 11 points, and I l L 1 failing at 14 points, so Zone OCR and doing a bias in favor of numbers or letters is the only fix for when it's mixing small l and the number 1, or capital O and the number 0.

For 11 point the only fonts that performed well consistently were Tahoma and Consola. Consola read zeros as small a's very consistently, so you could do a fix in Pattern Match and use that. Tahoma read O's as 0's.

At 14 point the zeros and capital O's read better, but almost all fonts failed on small L and the number 1.

With OCR there are more improvements with increasing the size of the text rather than changing the font.

Hope that helps!