It is indeed quite a dilemma when deciding on a standby generator. If you are any where near being a SHTF planner or being prepared for a long outage or breakdown of society, it's diesel all the way in my opinion. If your requirements are standby power for a couple of days or a bit longer, the usual 3600 rpm generators will be fine. They are designed for a run time of 200 hours a year which probably covers 90% or more of the average need.
That 200 hours a year limit is set by the EPA. There are different emissions requirements for standby vs. non-stanby generators. Those 1800 RPM standby sets will run WAY more than 200 hours per year. The manufactures just have to say that so the gensets are not mis-used. There is a new market for low hour units, think 3600 RPM diesels, these units are not designed to live as long at full load. They will still get you through an outage but we are talking hundreds (couple thousand hours) of hours of life vs. many thousands for the 1800 rpm units.
For example a rental genset (no-standby) with a built in trailer needs to be Tier 4 final with SCRs, DOCs and DPFs. A crafty person could take your new genset, bolt it to a double axle trailer and use it in a rental application for about half the cost and have it work just as well if not better because it doesn't have all of the after treatment. Here in the US, the department of transportation shuts these homemade units down for not meeting DOT rules but in other countries a lot of generators get bolted to old boat trailers and run for many years as rental units.
Here is an example of what the EPA does not allow here but you see a lot of in other countries.