I did a 30FG roll too:
That's not bad but not that good. I wanted girls like Mint or even another Pink-Miko. But I got a not that bad crit girl. But... my crit team is already full and the only girl I can change (Yukata Japanese Apricot) is already changed by Halloween Herbaceous Peony. she is still a new gold and a new pierce for my whaleship.
edit: for the chose your 5* stone, juste take your waifu. Or, if you don't have waifu or if you think more in term of use, take a really good and useful girl. Some of the bests for me are:
Camelia (very good in almost every kind of team and well balanced). But take the normal version, the the bride version. Camelia bride is... meh.
Cymbidium (THE best gold in term of ability with the awesome skill activation x2 for all. But she is weak stat-wise)
Justicia/Flamigo Plant (really nice skill activation girl with counter ability when bloomed)
Pink - World's Flower Shrine Maiden version (She is THE BEST counter 5*. If you want a counter team, you just NEED her)
Wax Vine - Christmas (well... put her with some other crit girls and she will kill everything. Just look mine! She is a monster)
Well... that's lot of slice girls but I guess that's all. There is a lot of good girls but, for me, they are just the best for what they are supposed to do, alone or as wonderful support.
But if I can give you an advice, just look at the 5*/6* you already have and try to make some synergy.And then, shoose the girl you need to complete that synergy.