IMHO you want as much inverter as your wallet will allow. As you step up in inverter size you can get away with running more things without stretching the inverter too much. Remembering of course the battery capacity you have, when you recharge etc.
As a general rule the larger the inverter the higher the charging amps back in which can mean shorter generator runs, less generator fuel, etc. The Magnum brand for example, 2000 charges at 100 amps, the 2500 charges 120 amps and the 3000 charges 160 amps. When I'm running my 10kw genny to charge batteries, I want to get as much out of it as I can for as short a time.
It's been a while since I priced inverters which was for my boat at the time, but the increase in cost for capacity was pretty reasonable at the time even if you don't plan right now to use all its capacity. Looking at just one site the price of a 2000 is $1119, 2500 is $1279 and 3100 is $1479. $360 for 50% more usable capacity.
Of course much depends on how you use the inverter also. Dry campers would get more benefit from recharge capacity than someone who goes from park to park and just wants to run the microwave without starting the genny. If when one of mine goes to the big copper mine in the sky, a 3100 Magnum will replace it.
PS, don't forget the recycle value of your old unit.
Ken
