What is the Best time to switch employer from immigration perspective- H1B and i140 approved

I am working in USA on a H1B and have 3 years left on my H1B. My current employer is going to file i140 in premium in few days. At the same time, I am getting 2 very good offers from other good employers. Apparently, new employers are also agreeing to start a green card process.

  1. I am confused on whether I should let go off the current company’s i140 and change employers and start the process afresh starting from PERM with new employer.
  2. Should I abort the idea of changing employer as of now and wait for 6 months post i140 approval and then only think of changing employer.
  3. Even if I wait for next 6 months after i140 approval, then i will be left with 2.5 years of current H1B. So while switching the employers will I get a fresh H1B of 3 years with new employer ? (assuming new employer will apply for 3 years)
    The idea is at the point at which I switch , I want to have enough time so that new employer and myself are comfortable with starting PERM and i140 process without me getting into a risk of having H1B expired before i140 approval.