Well, I have collected every HD player with the exception of the Onkyo (basically a rebadged XA-2) and the RCA (a rebadged A1)- I even have all three of the dual format players, so I am somewhat of an expert I guess.
If cost is no issue, the XA-2 wins due to the upscaling with its Reon HQV processing and anaolg outputs in case you don't have a receiver that accepts HDMi. If cost is an issue, the A30 does a fine job and is not as pricey as the A35 (pic quality is the same, but the A35 has analog outs for all channels). If you want the best CD sound, good upscaling and analog outs but you can handle longer load times, the XA-1 is also great and can be had for a song. My least favorites- although still decent- are the A1 (slow and for some reason seems to not be as good on sound quality and upconversion as the XA-1 even though it is the same chipset) and the A2/A20 (these are OK, but the A3/A30/A35's are better).
Among the dual players, the Sammy UP5000 and the LG BH200 are both good. The Sammy even has the same Reon chip inside.
As with everythting, this is all just my opinion.