I recommend using Roserade. Shinx and Roselia arrive at levels 10 and 20, respectively, so using Roselia saves some experience in the early game and makes it easier to defeat Roark and Gardenia. Roserade's special attack is much higher than Luxray's. Luxray has higher physical attack, but its physical STAB has only 65 base power. This is the moveset I recommend. Roserade can't learn growth or petal dance, so make sure Roselia knows them before evolving.
Roselia -> Roserade @ poison barb/expert belt/choice specs
Ability: natural cure
EVs: 100 Spe
- stun spore -> sludge bomb
- leech seed -> shadow ball
- magical leaf -> giga drain -> petal dance
Also you should use Weavile instead of Froslass because Weavile has better stats.