Which one will provide more opportunity to work as an MEI?
When hiring resumes there are going to be 2000 hour ASEL CFI's lined up around the block. ME time has always been the key breakout factor when hiring is competetive, which it usually is after a downturn.
Also there is a bill in congress which will require airlines to place more emphasis on ME experience, although no details are spelled out.
My suggestion would be ASEL to 1000-1200 hours, then MEI to 1500, then get the ATP (also soon to be a requirement for airlines). Any less the 300 ME hours and you may not be competitive, at least that's the way it was last time.
Other than that...teaching at a 141 school may pay more, since they normally do formal 141 ground courses which you can get paid to teach. Ground in part 61 may be minimalist, or they may expect you to provide it for free (I refused to do this, my time was worth the same regardless if was flying, preflighting, or doing ground).