It depends on you and your cycling style.

If there are places were you wish you had a gear in between two that you have, you might be a candidate for more speeds. That's all that more speeds gives you--smaller gaps between the gears.

If that's never been an issue, stick with the seven.

Personally, I like the ultra-fine control over power and cadence that ten speeds (with a close-ratio cassette) gives me. Other folks I know and ride with will wear out one or two "favorite" cogs in their cassette, so they could do with fewer.