I have recommended the Grainger supplied Briggs and Stratton gen. set mostly because of cost and simplicity of design.
If money is not a factor i would agree with others that an Onan is a better quality unit. I have also installed a Generac set and have had on problems with them, they are about as loud and about the same cost as the B&S. When i ordered the B&S from Grainger i had it the very next day, another reason for recommending them. The idea is to have power available should it be needed and to do it without breaking the piggy bank. In reality Gen. sets don't get used that much, it's just when you need them you really need them. Around here some towns were out of power for 12 to 14 days and now that the big storm is over you probably won't need a gen. for a long time. Which is exactly why i like the idea of nat. gas or propane as the fuel of choice, it doesn't varnish up creating a maintance issue. These units do a weekly 20 minute runtime of the engine only and if there is a problem there is circuitry to let you know that manitenance is needed. Pretty nice units for the $$$. If you don't know about electricity and engines your better off having it installed by professional contractors that will be available for maintenance and trouble shooting when and if needed.
I think most electrical contractors would install your system for you for about $800 to $1000 plus $4 or $5 per foot for wire, pipe, and labor to run between gen. and switch. This is just a ball park, cost will vary depending on locations and complexity of the install. The longer the run the bigger the wire size should be. The last one i just installed i used # 6 THHN wire in 1 1/4" pvc pipe on a 7kw unit, we installed the unit a 150' from the house, don't want to have to worry about voltage drop. That doesn't cover the cost for ditching and fuel hook-up usually done by others.