>> While the PCUSA now claims to be hierarchical for litigation purposes, true Presbyterians are not. <<
Who's the true Presbyterian? The name itself refers to a hierarchical structure, of Kirks, Presbyters, and General Assemblies, even once having synods. You might better argue that while Knox envisioned a Reformed Church, the Church of Scotland is, instead, very hierarchical.
That's easy. Those who subscribe to the Westminster Standards. In the US, the main denominations would be ARP, OPC, PCA and EPC; there are others.
The name itself refers to a hierarchical structure
No, there is a connectional structure, with higher courts, but there is no equivalent of an Episcopal, Catholic, or Lutheran Bishop who can tell local congregation what to do. The only real threat is to break the relationship. Both the PCA and EPC have had local congregations leave over disagreements; there is no hierarchical control.