If I was to join as a 500 series tech knowing what I know now, I would go ACS. Simple reason, any AVN skills will likely require you live in a large centre like Montreal, Toronto or Vancouver to get the lovely jobs with Pratt and Whitney, SPAR etc. An ACS tech will have marketable skills desired in ANY industry. After 32 years I have zero interest in seeing another airplane when I retire. Now, If I was an ACS Tech, any machine shop, textile shop, welding shop for any industry, be it fishing, agriculture or heavy equipment etc would be able to use my skills. The best part is you would not have to live in a cesspool... I mean large city.
We are having a large problem keeping ACS techs for some of these very reasons. Some former fitters and riggers re-mustered to ACS during the trade decimation... er I mean amalgamation.
Regardless, as an AVN Tech you will pick up many skills and yes, you can go for an AME, I also know several folks who have done just that, picking up extra experience and quals at small regional airports as a part time apprentice.
Best of luck.