Having looked at oodles of tubes, most current 27" Schrader tubes seem to be about the same quality (e.g. acceptable), as I suspect these days they all come out the same few Peoples' Revolutionary factories in China. Ditto with 700C tubes (the size difference being trivial to nonexistent in terms of inner tubes).
The co-op where I volunteer has been receiving Mitas brand tubes made in eastern Europe. These tubes in general seem to be working OK for now, but the rubber seems stiffer and less resilient than the Chinese tubes (not just the wall thickness, but the butyl rubber compound itself). Not sure how well they will hold up in the long term.