SF magazines, whether they are in print or on the web, have an uphill battle, loosing readers at a rapid rate. Even the "big three", Asimov's, Analog, and F&SF, have lost most of their readers. Interzone is hanging in there, but it never had many readers in the first place, though its reputation for publishing some of the best sf is solid. On the web, SciFiction, which regularly won awards, was killed by the suits, who care about nothing but the bottom line, and who don't read anyway. That leaves Intergalactic Medicine Show and Baen as the top two webzines.
Your zine is not really in competition with the other magazines -- in fact there never has been any real competition among sf zines. What is good for one is good for all. The problem is that most people don't read short fiction any more. Short fiction was popular when people worked longer hours, and would read a story over lunch or before bedtime. Now, most readers read novels, in a big gulp, over summer vacation.
Still, I wish you luck.