^L&C had four seasons, from three different sets of producers. So it was only good (albeit inconsistently) for 50% of its run. As for Smallville, I think at least half its run was good (if flawed) -- seasons 1-3 were good and 8-9 were good, and I think at least season 5 was reasonably good.
And I haven't seen all of Superboy, but I think only its first season was especially weak. And I think most of the Reeves series is pretty well-regarded, although it did get lighter and more comical over time.
L&C was still pretty good in its 4th season, and I really wanted to see where the series would've gone in a 5th season. Really the worst Season for L&C that I found was Season 3, but that was when they had the frog-clone storyline.
As far as "Smallville", I found the first two seasons to be rather hokey. I never really watched the show on TV: I saw the Pilot episode and episode 2 on the VHS that Warner's released up here and I was really wondering why the second part of the "Pilot" did not connect to the first part (Warner's had edited the two episodes together into a single movie), so I was kind of turned off by the VHS. I did get the DVD's later on, but even when I watched the DVD's I never really found the show had a stand-out season. But if I had to pick "Smallville"'s best Season, it would have to be Season 4, but even then it barely gets that level as it was nearly as forgettable as the other seasons. The only Season that I really watched on TV was Season 8, but that was only for about 6 episodes: the season openers and finales seemed to have been the best episodes of the series, while the other 20 or so episodes of each season really went downhill fast and had a hard time recovering for the season finale.
"Superboy", did have a weak First season, but visually it, along with Season 2 were the most visually bright of the seasons. Seasons 3&4 tend to get darker in both storytelling and visuals with a lot more night shooting. And I think the brighter visuals of the first 2 seasons also gave Superboy that look of what Superman represented. (Warner's has released all 4 seasons on DVD, with Season 1 having been given a general retail release, while 2-4 were released via the Archive program).
The 50's series is also infamous for how the producers, for the last 4 seasons, reduced the number of episodes produced to 13 per season in order to pay for shooting the series in color, and I really enjoyed Warner's decision to release 2 seasons in one DVD set.
The 1961 Superboy pilot was released as a bonus feature on the Complete series release of "Smallville", but I've found the set really expensive to double dip on DVD. Now if Warner's ever remastered the first four seasons in HD and did a Blu-Ray release with the 61 pilot thrown in as a bonus in HD. (The 1959 Superpup pilot was released Superman 1977-2006 Blu-Ray movie collection---but while the first 20 minutes appeared to come from film, the last 10 minutes appeared to be from a 3rd or 4th generation VHS, which I found odd.)