AM sounds very nice, but don't expect it to clear up current interference issues. Usually, if you have little static on the background of the station, you have no chance of locking the HD stream. AM HD radio needs a lot of improvement.
FM HD is good. It does give you a good alternative. I prefer Oldies 107.5 HD-2. Another favorite is KHMX-HD2, I prefer it over KRBE and it's still commercial free. Another nice addition is Texas Country at KKBQ-HD2 as well. If you like Smooth Jazz, than KODA-HD2 should fill you up (I don't know how well it sounds since I'm not a fan of Smooth Jazz at all). KTBZ-HD2 is another plus, it helps whenever you get tired of listening to the same rotation every hour from The Buzz. Other stations with multicasting are KKRW, KUHF, KHPT, KAMA (Don't expect much from this station) and KPFT.
KLOL, KLTN, and KRBE simulcast KTRH 740 AM, KRTX-AM, and Jack 103.7 FM respectively.