New radio? TS480SAT or HX. On the HX, I read they can be setup to key 40-50 watts and swing to 200 watts on AM and have high level style of forward modulation, one guy said they can sound like a plate modulated radio, so take it what its worth. I have never used or heard one but this is what I gathered from online readings from owners.
For a used radio (in case anyone interested), I think the best sounding ham radio on AM out of the box is the Icom 706/MK2/G, sounds like a CB, I have used one for many years with the stock hand mic, modified, and also the SM-8 desk mic, which sounded really good and you get all the popular ham bands, all mode. I was able to get about 110-115 watts pep on AM from the 706mk2G on 15 volts from my astron if I remember correctly. No one could ever tell I was using a 706, they thought it was a Cobra 142 or 2000. My father currently uses a 706mk2G in his pickup and I talk to him across the country on skip and it sounds like I am talking to a guy with a Cobra 29 and a power mic. I just talked to him the other day and you would never know he's talking on a icom. There are other radios that sound good on AM, but if your looking for just the best/killer sounding station then get yourself a Flex SDR-1000 or a Flex 5000 and a proper computer to run it on. You can even use a touch screen if you wanted too. These are the best to use for AM as they have the widest bandwidth and lots of configurable sonic features, plus you can go shopping for a nice studio mic etc...
I want to also mention that with 3rd party dsp software loaded into the Kenwood TS-2000, you can get good am modulation. The kenwood ts-2000 has worse HF receive compared to the TS-480HX from what I read (and what I mean by worse, is less dynamic range for close powerful station interference and close frequency signals interference, like on a hot band opening), there is a diodes modification to lower noise floor and improve dynamic range supposedly for the ts-2000 to improve its receiver (never got to that before I sold radio), I have only owned the ts-2000 as for as kenwood and I did not think it was that good on HF compared to all the other radios and thats why I sold it, but I had a earlier model from 2001-2002 (when I first got it), I played with a later model from like 2012-2013 and it did perform better as they did firmware updates along the way. It sucked out of the box and needed the 3rd party dsp custom settings loaded in for the right audio tune.
From my online readings and gathering it appears the Icom 7100 has low modulation and am output power and so does the Yaesu FT-991 so I would stay away from these rigs (do some youtube video searches and you'll see the owner complaints etc) and go with the Kenwood TS-480HX, they sell for around $1100 new and they come up used from $750-800-850. My father is going to buy one and I will report back soon with how the radio sounds and performs on AM, both from the watergate and through the radio across the country on skip as he will be doing roughly twice the power of the icom 706 he is using currently.
If you want to know what the best radio for ssb is brand new (since that was part of your question), I would have to say Flex 6700. If thats out of your price league, the best SSB radio for the money on the market is the Kenwood TS-590SG. It has scored higher on the dynamic range than radios and receivers that have costed over $10K when new such as the Icom 7800 or R9500 receiver. I do not know how the TS-590SG sounds on AM, but I would assume it would be fine given that the TS-2000 and TS-480HX both sound good on AM, I would assume that the same audio circuitry or similar would be in place for the ts-590sg. I would expect to see probably like 50-70watts pep on AM because that is about what the ts-2000 does I think, if I remember correctly.