There's no hard and fast rule when it comes to crystals. Sometimes you get drawn to a particular crystal, sometimes it's based on the fact that you just like it's colour. It can be as simple as that. It also comes down to interpretation.
Someone may pick up a rose quartz for the obvious reason - love and compassion. They could use this crystal to attract new love into their life, or they could use it to bring more compassion and openness to an existing relationship. Or they could even use it while studying so they're kinder to themselves while working on something difficult.
One stone = many uses. It's up to the owner as to how they use it.
My suggestion is to go for what you are instantly attracted to. I've made custom crystal sets for clients and guaranteed each crystal they are initially attracted to is the one that they need. I've had clients who struggle speaking up in their relationship, and they've liked all the crystals that relate to communication. I've had clients who have had a tendency to excessively worry, and they immediately go for the crystals that calm the mind. For me personally, I have always struggled with self-confidence - and of course my favourite crystals are the ones that relate to the solar-plexus and anything to do with inner-strength and self-esteem. All the yellow stones!
And if you're still unsure, you can't go too wrong with the Love + Relationship Trio. We could all use a little more love in our lives! Well that, and it's just so darn pretty.