My opinion is that there're 2 main alternatives today : YAMAHA SW1000XG and EMU APS and each has its pluses and minuses. APS is a great relatively inexpensive solution for those interested in creation .wav or .mp3 rather than .mid files as the final product, since E-MU company does not declare APS's compliance to any well-established standard ( GM is not counted because its evident obsoleteness ), whereas Yamaha purposefully makes its product line in full compliance to XG standard, ensuring exellent level of compatibility between XG synthesizers of different generations and full controllability of EVERY synth and mixer parameters including realtime filters, envelopes, equalizers and effects' basic parameters through MIDI, and, what is more, XG provides nearly 100% Roland GS and GM compatibility on the low level, i.e. correctly process Roland sysex messages (F0 41...F7), has limited MT-32 compatibility and all these guarantees, that absolute majority of midi files ever created will sound correctly on SW1000XG.
However, SW1000 does not have sampling capabilities so far and this makes APS more attractive purchase for those who needs sampling.
Speaking about effect processing capabilities i'd like to notice difference in ideologies implemented on these two cards, APS's way seems to be a bit more flexible, but Yamaha boasts more quantity of effects...on the whole there are tasks APS is capable to cope with while SW1000 is not, and vice versa.
Well, i can not say unambiguously who is the best of them - if someone's task is creation music based on sampling principle, let this one could go with APS and be happy, however if someone interested in listening to MIDIs, in utilization alternative synthesis capabilities ( for example virtual acoustic, formant synthesis, FM etc. ) and needs flexible control via MIDI, then SW1000XG is the best solution, although somewhat more expensive taking in mind plugins' prices...