Look at it this way. You (likely) have more bad stuff in your water than just phosphate and silicate. You can use removers for what they make removers for, and they will need to be replaced fairly often, which will definately add up, and you'll still have bad stuff being introduced into your water. Or you can make do with tap water for now, which unless you have a nice reef setup will be just fine, and put the money you would have spent on the removers into savings. Then you can buy an
RO unit off of ebay for around $90 if I remember right and be set for a nice long time with higher quality water.
FWIW, I used tap water straight out of the faucet for about 9 months with a starter/softie reef setup and saw no ill effects. I now use an
RO unit, and do water changes approximately whenever the hell I feel like it, or around every 4 months or so, combined with an algae filter,
dsb, and very high tech prizm skimmer. My reef did ok with tap water, but is thriving since the changeover, it was well worth the $90 I paid.
But as for your original question, I believe they are all pretty much the same.