Harman P43 or XXV

As far as reliability they are extremely similar in reliability, not all but majority of the parts are the same for both stoves and they work exactly the same as far as the logic of the stove. I use to clean and service/repair pellet stoves for two years and the xxv vs the P series is a wash in my mind as far as cleaning. The exhaust fan is harder to get to when needing cleaned but this needs to be done only 1-2 times a year for the average user and at 1100sq ft you will probably not be burning too many pellets, unless it is a very leaky upstairs and/or you live some where extremely cold so most likely only once a year exhaust cleaning. I find the heat exchanger on the xxv easier to clean than the p43 since it is slanted but mostly vertical right in front of you, easier to see what your wiping off. Also I'd rather take off the back panels to an xxv than a p43, less panels that open up more of the back of the stove easier, kind starting to split hairs here though. Smaller ash pan on the xxv but honestly most pellets produce so little ash it is not a huge deal. I can't comment about the noise which is better or worse, just that they are both basically the same in reliability and ease of cleaning when it comes down to it in my mind.
The burning of decent to good quality pellets in a Harman can be done on any setting, low to high, for long periods of time with out seeing too significant a difference. I personally burn a accentra insert low to medium low all winter long and it is not a big deal or caused any real ash/burn quality issues.

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If your married, don't let the wife see the XXV. The rest won't matter.

I have a corner install (minimal clearance to well) and 1000sg ft of space. The XXV needs its guts cleaned out once a season in my experience but I have to pull the XXV out from the corner to work on it. I just didn't have the room to come further out into the living space. But if your space allows it, I would recommend it. But over all cleaning it in my experience is not bad. Takes a little over an hour venting and all if you don't stop and have a few beers along the way. You will be emptying the ash pan more often then the P43 especially with ashier pellets.

To the noise question, my XXV sits next to the TV as well. You will need to turn the volume up on the TV but not much.

As dhall28 mentioned, they are both great pellet chompers and basically use the same parts. Going onto a third full season without any issue.