Maserati. Hands down winner. Worst frame alignment ever. Their low end bikes were so bad you could not get the chain to run on the chain rings. The bottom bracket shells were put in at some severe angle in relation to the center line of the frame. I don't think they ever used a jig or flat table for building these frames. Junk. Junk. Junk.
I'd say Lambert was second.
BMA/6 bikes. I would not list any of them. Despite being cheap, heavy and sold at gas stations, hardware & department stores, they all had a certain minimal amount of function. I always liked working on department store bikes because there was so much room for improvement and the owners were happy to have them work at all. I think people have lower expectations when they buy a cheap bike. But when you go to a bike shop and buy what is presumably a better bike for alot more money, the owners want it to work. I think this subject is by default limited to companies that made a full range of bikes. Those that had good bikes but were also supplying cheap bikes to fill that market segment for their dealers.
The mid range Raleighs needed lots of work too. Raleigh never seemed to rinse out the frames after brazing. The bottom brackets would be the collection point of all the residue. It was quite common to pull the cranks and not be able to turn the axle with your fingers. We always found large chunks of what looked like dried bread. Some acid/flux reaction I guess. So every Competition, Super Tour, Gran Sports got the full bearing clean and regrease. And the all campy bikes too. Pro & International. Lots of extra work. And don't forget to true the wheels and glue the tires on.
Trek. Their early rims were too soft and light. We had many customers come back within days or weeks needing wheel rebuilds.
On the flip side, I'd nominate Panasonic as best bike ever for assembly ease and overall quality. They came from matushitu (sp?), same company that supplied Schwinn Letours for a while.
Rick Paulos Davenport, Iowa. World of Bikes, Ltd, Maserati dealer in the 1970s along with some 30 other brands. Raleigh, masi, maserati, atala, panasonic, lambert, fuji, teledyne, drake, triumph, robin hood, roberts, proteus, rampar, trek, specialized, nishiki, cannondale, peugeot, gitane, motobecane, windsor, lotus, colnago, donaldson, gazelle, batavus, various bmx, kuwahara, and on and on.