If you want the biggest screen, then Note 8 is the no-brainer choice.
If you can live with a slightly smaller screen there are a multitude of great choices.
Top of the heap in terms of phones is Samsung. They always seem to be ahead of the curve with features. Iris unlock, AKG speakers, wireless charging, IP68 dust and waterproofing etc, etc. Also you should note that the new S9+ is only 0.1 inch smaller than the Note 8.
Second would probably be the Google's offerings in the Pixel 2 and Pixel 2 XL. The Pixel 2 XL is very similar to the S9+ just with less features. Also costs less as well. Many people would argue that this is how Google really intended how the android interface should look like. Very steamlined interface with no bloatware from the manufacturers.
Third I would say the OnePlusFiveT. This is a phone offered from a Chinese company called OnePlus. It is not as feature packed as a Samsung (no IP68 waterproofing, no iris unlock, no wireless charging) but it is a fantastic phone for daily use. At $659 for a phone off of contract it's hard to say no.
https://oneplus.net/ca_en/5t
Huawei's new P20 is causing some rumbles in the phones world as well but I have yet to use it and can not offer a real opinion on it.
You ask where the best place to buy these phones are? Would you not be getting it on term from your cellphone service provider?