I don't know anything about Silver Keeper, but these are two entirely different programs. You are comparing oranges to lemons.
Given that Time Machine is part of your system already, costs nothing to use and works very well, I see no reason not to use it.
If you're dying to spend money on an alternate backup method, I'd suggest a donation to Carbon Copy Cloner would be money better spent, and it acts as a good complement to Time Machine (I use both). Again, as far as I know Silver Keeper is a wonderful program, not saying anything bad about it.