I also got two RP3300A with my scope (DS2072 with hw1.0, but only 4 weeks old), while two RP3300 were advertised. Now I really wanted some 1x probes aswell, so I complained a bit (a lot) and finally got 2 extra RP3300 sent home for free. I didnt have to send my RP3300A back. Where I bought my scope, they're asking 45 euro's for a single RP3300 probe! Don't think they made any money from me, I got a 10% discount on my scope (765 euro) and two extra RP3300 (90 euro), so I only paid +- 675 euro for my scope.
Now, since I've got both, I can also compare them! :-)
The RP3300A have a much better feel than the RP3300. Build is better and they're also better isolated. With the RP3300 I get some glitches in the signals when I hold them in my hands the wrong way (finger close to the 1x/10x switch, probably picking up 50Hz in that case). The RP3300A are also a little bit smaller and thinner than the RP3300. The RP3300 have this yellow cap, to 'shield' the ground when probing on a PCB, but it falls off way too easily (for both probes, do others have this aswell?). I don't have a high frequency generator, so can't compare the bandwidth. Strangely, on some pages on the Rigol homepage, the A are rated at 350MHz, while on others they are rated at 300MHz.
If I'd have to chose between the RP3300 and RP3300A, then I'd go for the A! I'm not going to use the RP3300 in 10x mode, the RP3300A feel much better quality and is better isolated, so the RP3300 will be only used for low bandwidth 1x probing.
Btw, I doubt that either the RP3300 or the RP3300A are very good at 300MHz, but maybe someone already tested the bandwidth.