Anywhere you can find the plants you want for the price you are willing is fine. However I'd first recommend this site, if you know a few varieties you want or even just want to try, go post in the WTB forum. I've received many great deals on here far cheaper than anything you could get elsewhere, granted some can come with snails which I didn't like at first but now I like them, and with patience they are manageable anyway.
I've recieved all my plants from this community and the quantity, price, variety, knowledge, and availability is all vast. Heck, the last order of plants I got was conpletely free, the sender even paid to ship it, that is rare but actually possible in this community.