I'd get strips that match the voltage you're actually using (they come in 5v/12v/24v/48v). As far as I know, they're all 5v LED's and they just wire the strips differently internally (using groups of LED's instead of individual - the higher the voltage, the larger the group.)
One problem with the lower voltage options is the strips start to dim the longer they are because of the gauge wire used in the strip, so you'd have to "power inject" them more often (such as providing power to both ends of the strip and even points in the middle). 48v strips can be quite long with very to no dimming (like over 100'). For 5v strips, you can start to get fading after just 15 feet or so.