For tobacco I have tried TFA RY4 double and Tab and like them both. RY4 is very popular and the Tab is a bit strong and might not be for everyone. I just ordered some Hangsen's tobaccos as they are very popular and presumably easy to mix and don't need any additives (AP, EM, ACV, etc. unless you want).
I subscribed to the "fruits don't need to steep or only need 3 days" and that might be true for some vendor brands or just fruit. If you add menthol or creme, etc, I have found a long steep produces "bold" flavor and also allows the different flavors to meld.
I started out with all TFA flavors and some people don't like them. They say they taste chemically or something. I haven't found that but I tried some juice that had been sitting for 2 months and it was way different from a 3-7 day steep. It changed color and had a deep flavor profile not present in the same un-steeped or quickly steeped juice.
Ultimately you will have to do some reading and experiment so buy sample sizes to start out.