Hi @Colin Riley,
Welcome to BP! Yes North Arlington and Garfield both have the right blend of MF housing stock with decent pricing and low enough taxes to make small MF properties work. Both have some benefits and drawbacks.
Commuting from North Arlington can be a little bit of a pain. Unless you leave very early in the morning, the bus commute can be very spotty. From Rutherford it can vary anywhere from 20 minutes (prior to 6:30AM) to 2 hours (after 7:30AM) depending on traffic and if a bus breaks down. It may only be certain areas but North Arlington bus service is DeCamp, instead of NJ Transit, which is not as frequent or reliable. With that being said, North Arlington is a great town. There are a lot of good restaurants, especially a few very good Indian places.
In Garfield you should be careful of where you buy. There was a major chemical spill in the 80s that wasn't properly contained so there is a large section near the Garfield train station where high levels of chromium have been found in basements of homes. It's designated as an EPA Superfund site but given the current administration's EPA head, don't expect anything to happen there in the next 3 years. Here's an article with a map of contamination area:
http://www.nj.com/bergen/index.ssf/2012/09/epa_to_...
At the very least, make sure you have properties tested for chromium in during the inspection phase. One other thing worth noting is that the train stops at the Plauderville station much more frequently than the downtown Garfield/Passaic Ave stop. In general the Plauderville side of town is much more residential and has a more neighborly feel to it. There are a few people on BP that have successfully house hacked in Garfield, one was a podcast guest. The values and taxes make it a very attractive place to invest.
Outside of Southern Bergen County, there's also Clifton, Bloomfield, and Belleville for towns you may be interested in. Taxes are higher in Essex county so from a numbers standpoint they are a little tougher to make properties cash flow. Good luck with your hunt and feel free to reach out with any questions!