This is hard to say, they are both pretty much in the same price class, have similar features. The EMU seemed to have slightly better reviews.
EMU Features:
* PCI audio interface
* E-DSP accelerated effects processing and mixing
* Zero-latency, hardware-based mixing and monitoring via included PatchMix DSP mixer
* 2 - 1/4" analog inputs (24-bit/96kHz, 111dB SNR converters)
* 2 - 1/4" analog outputs (24-bit/96kHz, 116dB SNR converters)
* S/PDIF I/O coaxial/optical (24-bit/96kHz)
* MIDI I/O
* Ships with ASIO 2.0 and WDM drivers
* Includes Steinberg Cubasis and WaveLab Lite, SFX Machine LT, and a trial version of Minnetonka's diskWelder BRONZE
* Works with most major PC audio and sequencer applications
M-Audio Features
* Award-winning 24-bit/96kHz digital audio card
* 2x2 full-duplex audio performance
* Gold-plated RCA jacks
* S/PDIF digital I/O with 2-channel PCM and AC-3/DTS passthrough
* 1x1 MIDI I/O
* Zero-latency monitoring
* Software-controlled 36-bit internal DSP mixing/routing
* Apple G5 compatible
APPLICATION:
* 24-bit/96kHz multitrack recording
* MIDI recording and playback
* Supports digital transfers; digital mastering
* A great card for LP/cassette-to-CD transfers
* Ideal for computer-based home theater and hi-fi systems
Includes Maximum Audio Tools software bundle
They are both pretty good sound cards and it would be wrong for me to tell you "get this one", When choosing a card you should see if the cards features will fit around your working criteria. Both seem to have similar features. But if I had to make a choice it would be the M-Audio. I heard good things about that card.
Good Luck!