Peter because he was able to wrangle the boyers and push Russia towards its first modernization, created a real army and navy, looked towards real strategic survival by going south towards the Black Sea, all while fending off numerous assassination attempts, the orthodox church (which sometimes supported him and sometimes didn't) and various other achievements.

He didn't always succeed, but I believe he was extremely far thinking and moved Russia towards its future empire under both the monarchs and the bolsheviks.

Catherine for some obvious and not so obvious reasons. I mean, you have to give it to the lady, she was a nobody outsider in the court and wrangled it into the crown of an empress. She kept the men jumping to her tune, made the army grand again, kept the empire together and basically whipped the boyers and the church into obedience. Oh...she made Russia rich. took the fight to the Ottoman. Gained the Crimean peninsula and finalized Peter's drive to get access to the Black Sea.

then there is the whole arts and culture renaissance and the somewhat on again of again religious protections. Seriously, you cannot have a list of "greats" without Catherine the Great.

Elizabeth I. 45 years on the throne, fending off all sorts of power grabs and intrigues. kept her head. navigated the perils up to and directly after the ascendancy to the thrown. Various assassination attempts. Defeated the Spanish Armada. Kept a post Henry VIII England together. Over saw the expansion of the British Empire, exploration to the United States and colonization. Kept the French at bay. Shakespeare. Marlowe.

None of these were perfect, but they were very good when it was needed.