No company -- 121 or 135 -- will "look down on you" if you're not a CFI. The primary advantage to becoming a CFI is that you have to know the material in order to teach it, and, especially for a CFII, it's a lot of the same material you'd be asked on an airline interview. As said before, they're hurting for pilots too much to be snobbish about where the flight time comes from (as long as it's legal).

If you have a connection to a job which is not instructing, and will get you the time/experience you're looking for, go for it. Instructing is just traditionally the easiest way to log time, make a living, network some, and prepare for the interviews.

Some other options are pipeline patrol, traffic watch, skydiving, and some Part 135 operations such as Air Choice One and Cape Air will hire FOs with around 500-700 TT.