Look at the eye stalks, if they don't really taper very much, and have fairly large round eyes on the end that have distinct rings of colors in them (sometimes blue) around a black pupil then it's more likely a conch. If the eye stalks are tapered, end in a tiny point with a tiny eye or no visible eye, it's more likely a whelk. Whelks are often predatory and not usually considered "reef safe".
And just to be safe if your going to collect live critters in Florida you need to learn to identify the Queen Conch. These are a protected species and illegal to collect.