Hello Om, since you say that quality is most important there is almost no choice, you must see the work of Dolly and Lilith Heart. It's so different from all the other garden centres as their plant work is all art work. There is almost no other garden centre that does it this way and it shows. If you want the best for a truly immersive role playing experience, I'd say look no further than Lilith Heart.
Oh and Arctic Greenhouse have lovely sculpty house plants, primmy but worth it
So my list is :
Heart Garden Centre - absolutley awesome virtual plants and trees
Arctic Green House - gorgeous sculpty plants and flowers
Kriss Lehman's Botanical - lovely trees