100W MV lamps. The ones lower than 100W are bad with dimming too but they were never used for street lighting in the US and Cnanda (other than for some rare post top installations or privately-owned lighting). The 100W MV lamps have a thinner diameter arc tube when compared to other mogul base lamps and of course it's shorter than higher wattage lamps too so naturally they blacken faster than higher wattage lamps too. They also have smaller electrodes too so they generally didn't make it as long as their higher wattage counterparts. Joe Mauarath Jr said after the mid-60s the 100W MV lamps were "crappy", specifically the Sylvania ones. He said after only a few years they'd dim out, much like today's mercs. 175W+ lamps remained good in in terms of light output through the 70s.
The 80s GE MV lamps were noticably much worse than ones from the 70s with dimming out rapidly. Even GE's post-Bonusline mercs still maintained fairly good lumen output until the 1980s, when GE started focusing more on developing MH lamps and making the final improvements on HPS lamps. At this time GE was having issues with their new 50W HPS lamps (50W HPS rolled out in 1980). The arc tube seal kept failing on them. They were so bad that GE offered free replacements for hundreds of failed lamps in a town in Massachusetts (and I'm sure others as well). Those replacements also failed early and GE yet again offered free replacements, which apparently held up. I'm not sure if their other 80s HPS lamps were bad or not but their low-wattage HPS lamps were excellent in the 90s, right at the peak of the HPS changeout. I know a lot of 50 and 100W HPS fixtures with 90s GE lamps in them, still going strong! I've noticed that GE's mid-90s 250W HPS lamps have an issue with not warming up all the way (they get stuck in the LPS-like deep orange-gold glow). I'm thinking that might be a sign of the outer vacuum lost (arctube seal fine, but the outer envelope seal broken). HPS lamps need the outer envelope vacuum to warm up all the way because under normal atmospheric pressure, the arc tube can't retain enough heat to warm up. With MV lamps, the vacuum only serves (as far as I know) as a heat buffer since the arc tube runs really hot. The vacuum in a HPS lamp serves the same purpose, as HPS arc tubes run at 1000's of degrees celcius but without the vacuum the lamp can't warm up enough to create intense heat anyway. In the mid-2000s, GE's mercs has issues with the arc tube seals but I don't know if it's since been fixed or not. I don't know about their HPS lamp quality but I heard it wasn't too great either a few years ago. NGrid uses Sylvania lamps now so that must say something...
As for Westinghouse lamps, they really remained top-notch all the way through the 80s when Philips swallowed up their lamp division. Their 100W mercs also had the dimming-out problem but it's just the design of the lamp that makes it prone to blackening faster than 175W+ lamps. 175 and 250W mercs share the same arc tube diameter (250W is just longer). 400W MV has a wider and longer arctube. I think 700 and 1000W share the same diameter arc tube but I don't know. When Philips took over, the MV lamps were soon degraded to the equivalent of GE's MV lamps or maybe worse. Philips' HPS lamps remained pretty good (HPS was the craze back in the 80s and 90s so HPS was the equivalent of what LEDs are to Philips now) but once the Alto generation of HPS lamps came out, their quality went down the tube. Since the end of the 90s their MV lamps are royally sucked too, the arctube frame welds are poor and normal vibration from being in service often breaks the arc tube welds so the arc tube ends up just sitting at the bottom of the envelope.
As for Sylvania, they really weren't used a ton here so Joe Maurath Jr hasn't mentioned much of them to me other than the fact that even their 60s 100W MV lamps really sucked. The electrodes were even smaller than GE's or Westy's and they dimmed much faster. I have a 70s Sylvania 100W BT25 cleartop that's about as bright as a 40W incandescent. Joe gave it to me with the M-250A. He said he was surprised that it still works, as it was pretty typical of those lamps to just go out after "X" number of years. I think their 175W+ lamps were fairly good. Never heard anything bad about them so they weren't terrible but never heard anything great about them either. Like I said, they weren't used much here (only when NEES or EUA ran low on lamps and GE or Westinghouse couldn't get out a shipment fast enough lol) so most of Joe's Sylvania lamps are from municipal utilities or from trades or from auctions, etc. I have a few 80s Sylvania 50W HPS lamps and notice that they take forever to warm up (as long as 15-20 minutes like a LPS) and they don't seem quite as bright as some known-working 50W lamps so I'm guessing they, too, had issues with their early 50W HPS lamps, which is odd since you'd think everyone would have made their 50W lamps like they made their 70W and 100W lamps. EUA always used 70W HPS though, never used 50W HPS. And NEES used 70W HPS until the early-to-mid 90s until the HPS takeover, when they used all 50W HPS and no more 70W HPS. I guess they took notice of the 50W HPS failures and stayed clear of the until quaility was improved.
Overall, I think Westinghouse made the best lamps regardless of the type (HID, fluorescent, incandescent, etc, though incandescents seem to have been consistant across the board up until the 90s when most production was moved to Mexico or China, though the Mexican GE incandescents were still decent, the Chinese ones totally suck though). For modern lamps, I'm all Sylvania for incandescents and halogens since the GEs just suck and the Philips don't seem great either. For fluorescents I prefer GEs but have nothing against Sylvania fluorescents. For HID, Sylvania makes the best HPS, MH, and MV lamps IMO but for MH and PSMH Philips is great, namely for their ceramic arc tube MH/PSMH lamps. Philips makes the best CMH lamps IMO.
