Sound Blaster was the established brand for sound cards. Nobody was able to compete with them. They had the market penetration / marketing and were leading massive consumer market development. There were many cards that were a lot worse, some the same, some a little better and all cheaper. There were a few that were much better but also a lot more expensive.
And again: a sound card is not necessarily a sound card. A MIDI card is separate from a FM / samples card. Most valuable are the MIDI card: MPU-401s, daughterboards (DB(50/51/60)XG, SCD-10/15, SCB-7/55) / wavetable cards (RAP-10, SCC-1(A/B), LAPC-I, SW60XG) and RAM based MIDI cards with special chips (GUS / Mediatrix). Early FM / sample based cards are also valuable: CT1300/10/30/50, CT1600/10/20/80/90, CT2600, CT5320/30.
Once you get to the Windows 95 generation cards the value usually drops because so many were produced / are still available. Plus sound became generic and standardized through Windows 95 drivers. And HDD / CD-ROM / DVD space became so cheap that MIDI was no longer required for good music in games: it was just recorded / sampled.
A good rule of thumb is that the early sound cards that were produced in lower volume with high quality are the most valuable. Other early sound cards without a brand name (e.g. generic clones) or those produced in large volume (CT1600 comes to mind) are less valuable. Other mid period sound cards with exceptional quality and/or cult following (GUS: demo scene) with low volume are also somewhat valuable. Cards made in high volume in the mid and late period (and especially generic cards with "Crystal" chipsets for example) have little to no value. SB16 with ASP/CSP chips are somewhat more valuable than regular SB16s for bragging rights.