As far as I have seen, it is almost a consensus here on the forum and in other political forums that Leonid Brezhnev was at the best a mediocre leader that led the USSR into the era of stagnation, the arguments differ, from blaming him for his hardline polices or the massive military spending. Based on that I ask you: What would be the best leader to take over the USSR instead of Brezhnev?
Well... I think the whole "reformist" and "hardline" terminology used in the West doesn't really fit actual Soviet politics.
Actual Soviet politics, so far as I understand it, had more to do with who your friends were. So the same man could back liberalizing measures one day and be the hardest of hardliners the next day, depending on how that policy affected his friends, his patrons and his clients. It's not to say the Soviet politicians didn't have strong ideas and weren't motivated by their principals. But where those ideas and principals are seen though the lens of party loyalty by politicians in Western democracies, in the Soviet system, principals and ideas were seen through the lens of the patronage network.
So I don't think it is right to say that Brezhnev had hardline policies. And I'm not sure he was really that mediocre. Had he died between 1972 and 1977 he would have been acclaimed as a great leader who oversaw a great rise in Soviet power and a great improvement of the prosperity of his people. Of course, from about 1974 on, his mind was too decayed to really provide leadership and the country drifted until November of 1982.
Anyways. As for who a better replacement would be, I think the big question is: who has a healthy mix of caution and good health. That doesn't leave many options. And all the healthy and cautious people are also the ones who seem to have desired power the least.
Kosygin died before Brezhnev in OTL, and besides that, I think his reforms either went too far or not far enough (depending on your perspective) and if fully implemented it's too easy to imagine the USSR drifting into the same sort of trouble places like Poland, Yugoslavia and Hungary had. Despite that, I think that Kosygin being important in any post-Khrushchev regime, he did have good ideas and he had a rare perspective on Soviet problems (being a manager by training, rather than an engineer as most of the Politburo were). Kosygin doesn't seem to have had the ambition that Brezhnev did, but he was definitely a contender for a while (and was treated as being more dangerous by Brezhnev) so he seems to have had desire for power at least.
Gromyko (lived until 1989, seems to have been sharp to the end, or at least was sharp until very near the end, marked by a remarkable sense of duty and service, spoken of with great respect by his friends and enemies at home and abroad) could be an interesting leader. Of course, he was such a loyal servant that it is hard to see what his choices would have been if he'd been running the country and it is even harder imagining him getting the top job since he seems to have exactly zero interest in it. I'd love to know enough to write an ATL with Gromyko as leader, but as of yet, I am too ignorant. It's worth noting, along with Brezhnev, he was one of the big opponents to going into Afghanistan.
Suslov is another interesting one. The chief ideologist of the Party, like Gromyko, a man who seems to have been motivated by service rather than ego, also somewhat of a questionmark. He kept himself away from the public stage. He does seem to have been one of the big fish in the Soviet regime really since the Khrushchev era. His office was considered to have been the best office of all of the Politburo members - and he seems to have had absolutely no problems keeping that office. I've read conflicting reports on whether he actually wanted power. He was one of the contenders for the top job during Khrushchev's rise and during Brezhnev's rise, but at least when Brezhnev was rising to power he doesn't seem to have pushed too hard for power. In both power struggles, he was able to sell his cooperation with the eventual winners for high prices. However, I've read more than once that he had no ambition for the top job. So was he participating in the power struggles only to ensure the winners had to pay him well for his eventual support? Hard to say. He was also rumoured to be Stalin's pick for successor during Stalin's last years. Suslov also seems to have been pro-Afghan intervention (which could be good, since going in earlier would mean less opportunity for the Afghans to let trouble in the country snowball, and could be bad, since the Soviets themselves could still cause problems to snowball if they are neck-deep sooner). Suslov died in 1982, but he seems to have been wickedly intelligent right to the end. Suslov was also the patron of Andropov, in my view the best chance the Soviets had of "pulling a Deng", so while Suslov himself may not be a "good" successor, he could pave the way for a more secure and stronger Andropov leaderhsip.
Nikolai Podgorny is another possibility. He was a key ally in Brezhnev's coup against Khrushchev, Podgorny was the Second Secretary of the Party and controlled the Organizational Division - potentially a strong foundation from which to launch a bit for supreme power. Podgorny also seems to have had plenty of ambition (more than Kosygin) and also seems to have been more of a liberal - reputedly even more liberal than Kosygin though I am not sure what policies he favoured. Before Podgorny helped Brezhnev out Khrushchev, he was a close ally of Khrushchev. Podgorny is probably the most likely to gain power after Brezhnev. In OTL, he lived until 1983, though I am not sure how sharp he was before the end. He at least seems to have stayed sharp longer than Brezhnev.
And of course, there is a good possibility Khrushchev can out-manoeuvre the coup against him - Brezhnev and his allies skirted disaster at several points. Khrushchev in OTL fell into misery after his ouster and died in 1971. I suspect he would have stayed sharper longer had he retained power, but still, he likely would die before the 70s ended. Khrushchev's love of high tech solutions probably means good things for Soviet R&D and bad things for Soviet overall military power. That could mean that his last years save his reputation, as investments in R&D have more time to bear fruit and his willingness to shake things up when they needed to be shaken up (and even when they didn't need to be shaken up) would leave little room for Brezhnevite stagnation to set in. Khrushchev could also lead the USSR into worse crisis by leading them down the path of half-baked reform that led Eastern Europe into trouble. It's hard to say. Certainly, he's likely to die at a good time, leaving the stage in time for new people to come in just as the problems of the 80s are starting to show on the horizon, but early enough new people could consolidate power before they had to implement reforms.
fasquardon