In all likelihood, Stalin still comes out on top.
Remember that Lenin had appointed him General Secretary in April 1922--one month before the first stroke. This appointment will almost certainly be confirmed by the new "collective leadership" after Lenin's death. After all, it was what Ilych wanted--and some of the Politburo members may not grasp just how powerful this new office will become. Even if they did, they would prefer Stalin to Trotsky or Zinoviev-Kamenev. Trotsky was viewed with suspicion for all sorts of reasons: his status as a relative newcomer to the Bolshevik party; his intellectual arrogance; the fear of him as a potential "Bonaparte' etc. Zinoviev was also personally unpopular and still had to live down his opposition to the October insurrection. Anyone could quote Lenin's years of denunciations of Trotsky (and Trotsky's equally vehement attacks on Lenin) or his characterization of Zinovivev and Kamenev as "strikebreakers" at the time of October. There were no similar denunciations by Lenin of Stalin--the "Testament" of course had not been written in this ATL.
IMO if Trotsky had any chance to be Lenin's successor, he blew it by going against Lenin in the "trade union dispute" of late 1920, where Trotsky advocated the militarization of labor and the open stratification of the trade unions. This led in March 1921 to the removal of Trotsky's ally Krestinsky from his post as "responsible secretary" as well as from his Politburo and Orgburo positions. It also fostered a negative image of Trotsky in the Party. I discuss this at
https://groups.google.com/d/msg/soc.history.what-if/R8y9UR6NylI/Vy6EPVvx7_MJ
As for the possibility of Trotsky coming to power through a military coup, I agree with Roy Medvedev: ""It must be said quite emphatically, however, that at the time of the discussion in the party there was never any real threat of a military coup, if only because the Red Army was never just a 'docile' instrument in Trotsky's hands. Trotsky could rely fully on the soldiers of the Red Army when he gave the order to march on Warsaw, but he could not have raised the Red Army against the Central Committee and the Politburo..." See my post at
https://groups.google.com/d/msg/soc.history.what-if/EAA2ui89o8I/SINb3uPQ9sUJ As Robert Service wrote in *Trotsky: A Biography* (p. 326): "Could Trotsky have used the Red Army to secure his return to ascendancy? He would need to have been a different kind of politician even to make such an attempt. He had already told fellow leaders that he did not aspire to a personal paramountcy; and even if he had not been frank with them or himself, it is doubtful that he had the skills to put together an armed coalition that would have done the job for him. The Red Army high command was riddled with ambitious rivalries and there is no evidence that Trotsky was the darling of any group of commanders. .." Admittedly, Service is talking about 1924, when some political commissars loyal to Trotsky had already been purged; but even in 1922 a coup would have been a very risky proposition, and one that Totsky was unlikely to attempt.
(One other disadvantage of both Trotsky and Zinoviev was their Jewish origins. The leading Bolsheviks--including Jewish ones--despite their professed internationalism, were well aware that anti-Semitism was still widespread in Soviet Russia...)
In fact, I would say that, in general, what-ifs about the USSR in the 1920's pay far too much attention to Trotsky as possible leader. If we are looking at alternatives to Stalin, I think that either Zinoviev and Kamenev or else (in 1928) Bukharin and the "rightists" had better chances of coming out on top than Trotsky did.