I have a life-long ambition to start collecting Les Paul Juniors, especially one from each year, preferably one in cherry red. I'm just wondering what era of Juniors were considered the best, did they have a slump at some point and generally how much are we talking about money-wise for the vintage ones?
At the risk of the answers to this question being too opinion-based, it appears the golden-age of the Les Paul Jr was during the years of it's original production 1954-1963. This would be ignoring the later reissues and variations.
I base this statement on this article, from vintageguitar.com, in which took place a friendly contest in order to determine which Les Paul Jr had the best tone... 14 guitars, out of 40 from that time period, were selected for the contest; all being played through a regular voicing Liverpool version of one of Ken Fischer’s Trainwreck amplifiers. Out of which:
one ’57 single-cut, one ’58 double-cut, and two ’59 double-cut TV models advanced to the final round.
The selection of the guitar with the best overall tone of final four was actually deferred to Mountain guitarist, Leslie West (which is funny that he is the guitarist that you reference in the comments, Tetsujin. Apparently, his Les Paul Jr is a single-cutaway from '56.)
Leslie West actually gave 2 separate auditions of the final four contestants through 2 different amplifiers before:
selecting the 1959 double cutaway TV model bearing the serial number 9 9014 as the Junior with the best overall tone.
As far as pricing, you can find some of the newer reissues and variants for under 1000 dollars/euros. For the originals, your pockets will need to be pretty deep, I'm afraid: