I'm trying to decide what brand / manufacturer of water softener system is best.
Who do you recommend?

We like any system that uses the Fleck 5600 Econominder Valve.

And these are not sold as a "Brand".

There are only a handful of "true" manufacturers of the Valves and Tanks.

Pentair Water ( maker of Fleck and Autotrol ) is the largest, but sells "NO SYSTEM" under "Their Name", but every one uses their Valves and Tanks.

see:

Identify Brand of Control Valve

The important thing is serviceability and parts after you own the unit.

They all work great at first, but they all need a few parts replaced, and can last for Decades under normal conditions.

Avoid proprietary brands, like Hague, Culligan, Rainsoft, Kinetico, Water Boss, Ionics and a few others that "lock you in" to the local dealer for parts & service.
Generally the proprietary "brands" will cost more up front, and usually a lot more for any repairs later.

see:

Fleck 5600 Econominder is Recommended Valve

and

Complete Water Softeners For Sale

and

Water Softener Size System Recommendation

**** CUSTOMER QUESTIONS - Andrew's Reply / Opinion - posted March 2nd, 2016 ****

1) Previously in this email chain you recommended the "5600 Econominder or equivalent Hankscraft model". Please explain the differences in operation between the two models and provide your experience with the each regarding lifetime, failure rates, warranty, country of manufacture, and programming steps. If there are no differences in any of the listed items above, please justify the difference in price of $70 between the Fleck and Hankscraft valves.

** No operational difference. Same 5 year warranty. Both made with many of the parts from China. Both brands analog version are "programmed" the same way.
See:
How to Set Meter without the People or Hardness Labels on Fleck Econominder Valves

Fleck valve cost more because they are the "brand name", but the quality of the Hankscraft is slightly better.

I have used the Fleck 5600 since I first got in this business in 1989.

We started stocking and selling the Hankscraft only after 4 years of evaluation. The product and the company have proven themselves to me.

The design ( using Piston & Seals ) has been used since 1980, and is the # 1 valve design used.

2) My unit is a downflow unit. Please explain the difference between a downflow and upflow water softener.

* It references the direction the salt water travels when regenerating. The standard method is downflow.

Upflow is slightly more "efficient" ( about 5% more ), but the valves tend to get "gummed up" on well water sources, as the process pushes everything UP into the Valve Body, instead of DOWN and out the drain during the Regeneration Process. We do not sell or recommend "Upflow" brining for that reason.

Also, please indicate which recommended model works best with a downflow tank and why.

* They all work the same. It's pretty simple.

Reference,

How_A_Water_Softener Works