I am fortunate enough to be in Atlanta where I have been able to play both amps. I played a prodigy today and put it on layaway. In no particular order of importance here's why:
1. Weight- 30 lbs. vs 49, plus the Mesa is more compact and sturdy feeling.
2. Power- The Mesa at 250 tube watts is definitely louder than the Fender at 100. I could hear a noticeable difference through a 410.
3. The half power option on the mesa at 125 watts is more usable as a gigging bassist in smaller rooms than the 25 watt option is on the fender. The 125 watts still is quite loud and full sounding, probably louder than the fender at 100 watts. I tried them in two different stores, so I couldn't A/B them.
4. Tone- The Mesa's tone seems more harmonically rich and 3D, but that could be subjective, since I just played the Mesa today. I was wowed by the Fender's tone and Flexibility also.
5. Reliability- When I went to try out a Fender, I was looking to play a 300. The 300 that they had, although new, couldn't produce any sound and the bias lights kept cycling through and one of the guys let it slip that "another one is doing the bias thing"
That gave me a moments hesitation due to the new auto bias feature on the Fender Super Bassman Series.
6. Size- The Mesa will sit perfectly on any of my cabs, its about 17 inches wide,9-10 inches deep, 8 inches tall, just guessing from memory on the size.
7. Look- The Mesa looks COOL!!! I love Blue.
Both are great sounding amps and I am sure you'd be happy with either.
The Bass is not a big guitar, it is a unique musical instrument. It should be a drum, a flute, and a chainsaw.