There is no such thing as a bad Dual, at least not among the ones built since the 1960's. But, some are better than others. You also need to know what purpose the unit is being put to. Are you going to play 78's? If you are, then the belt drives will not serve, and you will be restricted to the idler drive 10 and 12 series. For these, I suggest the 1219 the and the 1228. Both have nice low mass arms, and will work well with almost any cartridge, and will play 78's. You can get a separate cartridge slide for the additional cartridge for the 78 RPM cartridge. Or you can pick a cart that has the ability to take a 78 RPM stylus, like a Stanton or a Shure, and just change the Stylus.
I have had 2 Duals, a 1010 and a 1237. I used the 1010 for 78's and 45's after I bought my first Thorens in 1969. The only issue with the 1010 was the cartridge slide, which had to have the metal contact slides cleaned periodically. Otherwise you get erratic sound due to poor contact. Arm on the 1010 is not great and is pretty much restricted to cartridges that track at 2.5 grams or heavier. 1237 is a belt drive that is restricted to 33 and 45. But arm works great even with low tracking force in tne 1.5 grams oe even 1 gram range.
My kid sister has a CS505 that she really likes that works well with a Shure V-15IV, even with light tracking. But sjam is right. This topic has come up before, but I don't mind pontificating on the subject of Duals. The more we know about your particular desires, like the 78 RPM question, the better we can help.
And good luck from the old pontificator who had dual Duals,