i have installed many, many generators over the years, from huge commercial units to residential backups. In my own home i could have installed a 1800 rpm liquid cooled unit but i didnt want to spend the money on a unit costing 3x what a 3600 rpm generac system costs mainly because we dont get many outages any more (that may change tonight with snowmigedden coming in with 50 MPH winds). I service many older 3600 rpm generac units with 100's of hours on them and there still going strong. It all depends on maintenance. I just serviced one with over 2,000 hours on the meter.
That being said, air cooled generators are NOT designed for continuous use. There for emergency backup. On my unit, i shut it down manually during the day because i dont want it running if its not necessary. If its 4F outside, id let it stay running to keep heater going. Off grid people need a generator designed for off grid situations. Diesel 1800 rpm units are great, if you have lots of prolonged power outages. If you have 1 or 2 a year, i think a propane or NG generator is a great way to go. No need to mess with fuel storage or transfer.
Ive had a few calls to service Wenco generators over the years, and they seem like nice units. Have not done much with them, but look impressive. Whatever you plan on buying, get a parts diagram and so a search for major parts to make sure you can get them locally. Over the years ive had issues getting repair parts for alot of marine generators and European brands.