I think most of the information you need is covered, but let me throw my pennies in.
FLOW
Criminal if you're postpaid (no static bill within plan). Great if you're prepaid (cheapest calling rates). Data currently BLAZINGLY faster than Digicel. Better access to humans through customer service. Mobile software platform is "immature" in comparison to Digicel. Dropped calls when driving greatly reduced versus years ago. Voice/Data bundles a bit more expensive than Digicel.
DIGICEL
Great whether prepaid or postpaid (bills static within plan). Dropped calls when driving increased versus original deployment years ago. Voice/Data bundles with rollover seem to be the best available (JMD$2,000 credit for 2,000 minutes on-net and 4GB data). TBH - you're getting 4G to their radios but 2G/3G connection at times. Or no connection.
DATA
If data is what you need go with FLOW. Don't even consider Digicel.
VOICE
If you do more talking then go with Digicel. Provided your friends/family have Digicel too.
OVERALL
It comes down to preference or need. Personally I currently use Digicel primarily. Once my new (dual SIM) phone arrives it will be Digicel for voice, FLOW for data. Occasional calls with the FLOW if the person doesn't have a Digicel - but most persons either have both or have a Digicel. It's rare that someone only has FLOW.
FUTURE?
As stated, when both networks finish their upgrades and roll-outs for 2018-2019 the ground may be a bit more level in the mobile department. I hate them both for various reasons - but they each have services that I need. I'm yet to find a plan that does all I need within a reasonable price range. Maybe as competition heats up it will give birth to something. And Caricel don't look like they're going on with anything at the moment.
Hopefully this helps somewhat.
Knowing the solution doesn't mean knowing the method. Yet answering correctly and regurgitation are considered "learning" and "knowledge".