There isn't one.
On 'manual' you will lose the main benefit of cdist, which is automated transfers on feeder routes. If you don't need feeders, use manual distribution.
I have seen the problem you describe many times: cdist can't reliably assign freight cargo when you add a new route to a station that already has a route established. Eventually it will assign cargo to the new route, usually after about 3 months, but it can take up to about 15 months in the worst cases iirc. The 'solution' to that is to use separate pickup station for every destination you need to serve.
I run FIRS with asymmetric for freight cargos, and 'effect of distance on demand' set to 0%. It's not ideal, but I understand how to make it work in gameplay.
Fonso did spend some time trying to improve how cdist handles this, but it's not really solvable within current cdist afaik.
The thing is, I left my game for a coupe of hours (like 10+ years in game) but trains were still empty. I think I'll go with manual setting for goods. Though as you point I got multiple feeder stations, but it works wonderful with manual mode. Did I missed something?
CargoDist can keep you on your toes. In one of my longest running games (nearly 9 years in real life gameplay now!) I have to keep an eye out on my distribution centers that I built to manage cargo. Sometimes I'll add a new route from a DC to a town, and without any warning, some time later, CargoDist has decided to shift a bunch of traffic to it, leaving me with a fleet of vehicles queued up waiting for cargo for the older stations that aren't getting as much as they used to, leading to huge snarl-ups at my DC. I've got a backload of cargo that's expiring, my station ratings have tanked, my vehicle reliability is shot, everything has turned into an unprofitable mess.
Indeed, I think it behaves a bit buggy for my taste when it comes to goods. For eyecandy purposes multiple stations for delivering supplies is no way for me
BTW guys, can you tell me is there any GRF for default trains for FIRS set? I saw one, but it comes with built-in colors for some train wagons, which cannot be changed. I remember there was GRF which adopt default vans for FIRS, but uses old wagons.