On Tesla's 75th birthday in 1931, he was featured on the cover of Time magazine. The magazine requested comments from his peers, and Einstein politely responded: "As an eminent pioneer in the realm of high-frequency currents… I congratulate you on the great successes of your life’s work.” It was a brief and to-the-point birthday message from a gracious Einstein.
In the poem "Fragments of Olympian Gossip" that Nikola Tesla composed for his friend, George Sylvester Viereck, Tesla was very critical of the scientists of his days.
Tesla specifically calls out Einstein:
"Now a long haired crank, Einstein by name,
Puts on your high teaching all the blame."
In 1935 in comments to The New York Times, Tesla was critical of Einstein's theory of relativity: "...like a beggar clothed in purple, whom ignorant people take for a king."
There was no love between Tesla and Einstein. The story goes that when Einstein was asked how it felt to be the smartest man on Earth, he replied: "I wouldn't know. Ask Nikola Tesla". I have seen the quote often but could not track its origin. Put in the context of the relationship between Einstein and Tesla, if Einstein did use those words, it would make sense that it was done with sarcasm, rather than as a compliment. Tesla never accepted Einstein's theories, particularly his theory of Relativity, so his opinion probably was not very high. Tesla was more like Einstein than he could imagine, which was probably part of the reason he did not like him. Einstein was different from most other physicists because he said most of his ideas came out of his imagination, but in contrast to Tesla, Einstein had a thorough grounding in science and mathematics. Tesla's ideas came entirely out of his head and whatever other sources he might have had, whether or not from this world not. Tesla was not a theoretical physicist like Einstein. He was more of an inventor, and most of his inventions did not come through. It may come out of Tesla's naivety and lack of business sense or the opposition of others like Edison, so it is challenging to compare these two.