You are right about Trotsky being intelligent, but it's hard to say he was more intelligent than Lenin.
I think what Trotsky and practically everyone else in the USSR did not see up until the Great Purge of the late 1930's was how far Stalin was going to go in securing his own power. Trotsky did do a good job seeing though how Stalin was getting power around himself and Trotsky was one of the first major challenges to that.
Generally, American and Russian historians portray it as if Lenin died naturally, and Trotsky followed that trend without holding out the uncertainty.
Lenin was intelligent, but I think Trotsky's books sometimes delve a bit deeper than Lenin's, but I do not at all agree with everything Trotsky wrote.
Trotsky was decidedly wrong when he wrote against:
1) anarchists like Peter Kropotkin and Emma Goldman
2) the Serapion Society which consisted of the most authentic Russian writers of the 1920's who continued the anti-establishment traditions of writers like Tolstoy and Gorky
3) the Social Revolutionaries who won the national elections outright in January 1918 only to be butchered by the Bolsheviks wall street financed police. He anticipated Stalin in these things.
4) the ever so brief period of Caucasian independence. The Bolsheviks continued the oppression the Romanov tsars Nicholas I and Alexander II began when they committed genocide against the Caucasian peoples in the mid-nineteenth century.
5) the Kronstadt Soviet.
(After Maxim Gorky [who represents the better part of Bolsheviks] requested American food aid for a famine in 1922, I find it amusingly characteristic of Bolshevism generally that when famine became excessive in parts of Eastern Russia that reports of cannibalism of recently dead bodies had surfaced, when Herbert Hoover replied affirmatively and sent his representative Walter Brown to initiate aid from the US, Maxim Litvinov was so suspicious of American treachery that he angrily laid down rules by which Russia would accept millions of dollars of aid to starving people. When Brown understood and outlined a plan, Litvinov shouted "No, no, no!" Many of Trotsky's words and actions have that same spirit of idiocy.)
Although Bukharin realized the truth about Stalin fairly late in the game, his writings lack the condescending tone that Trotsky often employs. Bukharin's books are great, but I find Trotsky especially boring and wrong when he writes about the Russian revolution. Trotsky's writing does not become worthwhile until late in his life when he's writing in the 1930's about things like Nazism, British history, America, or the Spanish civil war.
Lenin's books are too dry for me, but he was perhaps more open minded than Trotsky. Lenin was friends with Kropotkin and had read some of his books. Lenin even spoke with Kropotkin in person on two occasions after the revolution and listened to the anarchist's criticisms and suggestions even though Kropotkin opposed the Bolshevik revolution. That is a lot more than I would expect from many people today who have become unforgiving even to tactical enemies who have the same goals. I am not aware of Trotsky being so inclined.
Lenin's character goes a long way to explain his international popularity far beyond his circle of Bolsheviks. The same goes for Kropotkin's popularity far beyond his circle of anarchists of the pacifist variety.
Lenin was the middle ground of the Bolsheviks between Trotsky on the left and Bukharin on the right.
As far as assassination goes, I think you have to read the pertinent lines in both Trotsky's and Brackman's biographies of Stalin to appreciate my opinion. It is the knowledge of facts contained therein that gives me the confidence to assert that Stalin poisoned Lenin.
There are no historical proofs that can verify that Stalin was part of the Okhrana secret police.
If you have already read Roman Brackman's book about Stalin and still believe that, then I would be impressed and interested to hear your refutation - not to refute it, but rather to learn from your understanding. However, if you are unaware of the facts cited in Brackman's book before making such a denunciation of one of its central themes, then I would say you have a right to your opinion, but I'm not impressed.
I read several reviews of the Montefiore's biography of Stalin and discerned that it actually avoids Stalin's early years and contains hundreds of pages on trivial details of everyday life of the Soviet elite in the 1930's and 1940's like what Molotov preferred for desert and other useless soap opera rubbish.
Roman Brackman was born and lived in the Soviet Union while Stalin was in power. Simon Montefiore, on the other hand, is a British guy born several decades later whose reviews indicate he writes long drawn out ('War and Peace' length) popular books on people like Catherine the Great containing loads of mind numbingly boring, trivial, useless details.
Thanks for recommending Simon Montefiore, but I'll pass because I don't think he writes the kind of books that I read.
I don't mean to sound overly critical, but I sincerely believe that I would become less intelligent if I took the time to read Montefiore's books.