I'd tend to go with the same family of instruments; and, since Raymarine has the largest market share, I'd just go with them. I'd "oversize" at least one unit or two above their "recommendation" for your boat. Raymarine (and Autohelm before them, as well as other manufacturers) seem to size their recomendations for flat water and motoring.

Will a ST60 Plus Raymarine instrument connect into your exsitng ST60 instruments?

Regardless, I think the Raymarine probably has the most easily available parts.

(We love our Hydra units. The hydraulic Hydra Pilot is 13 years old. We have it driving a Hynautic ram because that unit is much more robust. I'm not sure about the newer units. The less expensive B&G units have gotten good reviews; however, I'm not personally familar with them. I believe it will cost you more; and, I'm not sure you'd get that much out out them.)