Probably the biggest decision to make on inverter selection is whether to get a pure sine wave inverter or modified sine wave inverter. You need to research the difference between them and decide which one you prefer. The true sine wave inverters are more expensive, but you get power that is identical to what the power company generates and avoid issues with non-function or poor function of electronics as well as gain efficiency when powering microwaves or motors. I opted to go the pure sine wave route. I also wanted an inverter with a good quality built-in battery charger to save both space and money instead of buying a separate charger. I needed a charger that could perform temperature compensation. The higher the temperature of the batteries, the lower the voltage you should use for charging. Good chargers are three-stage, meaning they have a high current bulk charge, then a slower finish charge, followed by a lower voltage maintenance charge. The charger should be programmable for AGM type batteries, since the charging requirements for these batteries are different than standard wet cell or gel cell batteries.
For pure sine wave inverter⁄chargers in the 1500 to 2000 watt range that I was looking for, there are several high-end manufacturers. These include Xantrex, Magnum, and Outback. Xantrex has purchased several other inverter manufacturers the last several years and includes a large and varied product line. There is also a second tier of imported inverters that can be purchased for less money. These brands include Samlex, AIMS, and Exeltech and generally cut some corners in their design (just look at the weights). I'd still seriously consider these due to the price savings, however, these imported models tend to not have built-in battery chargers, so if you factor in the expense of purchasing the charger separately, the savings are not so great. In the end, I narrowed it down to the following models (I included the best price I could find for each inverter):
Xantrex ProSine 2.0 ($1240 new, $750 factory refurbished)
Xantrex RS2000 ($1280)
Magnum MS2012 ($1359)
Outback FX2012T ($1532)
If you don't need 2000 watts, the Magnum MMS1012 (1000 watt) is a very nice unit. Also for a high quality small unit, the Morningstar SureSine 300 ($250 for 300 watts) looks very nice. If you end up buying an inverter without a charger, I recommend the Xantrex TC40+ charger ($314). It's the nicest I found during my research. Don't rely on your existing inexpensive 12 volt converter to keep your expensive AGM batteries up to snuff. The Parallax 7300 that came with my Roadtrek will put out 13.8 volts continuously. This voltage is too low to quickly recharge the batteries and is too high for a long duration float charge. While you can probably get by using this 12 volt converter as a battery charger, your batteries will be stressed a little more and may have a shorter lifespan.
You can download the user manuals for each of these inverters from the manufacturer's web sites. I recommend reading through all of them to get a feel for what features these units offer and installation recommendations. If I had to pick a unit purely on features, technology, and price, I'd probably go with the Xantrex RS2000. It's a brand new design and comes loaded with features. My problem with the Roadtrek, however, is limited space. After looking over potential installation sites, I decided that the space under the passenger side second row seat would work the best. We rarely used this storage space and it's fairly close to the existing battery compartments. Unfortunately, when looking at the dimensions of the various inverter units, the Xantrex ProSine 2.0 is the only one that will fit within this space because it is not as tall as the other units.
I ended up buying my ProSine 2.0 on eBay. I bought a factory refurbished unit because of the cost savings. It comes with a 1 year warranty (instead of the normal 2 year warranty that new units have). Otherwise, I'd recommend checking out the following sites for prices: partsonsale.com (you have to call them for prices), altenergystore.com, donrowe.com, defender.com, and scubasteve.biz. A Google search on any particular inverter should also give you many additional dealers. It seems that marine and solar energy applications are a much more common use for inverters than RVs.