This is a quick pyramid diagram I typed up! This is how I view physical bitcoin pieces and how I look at them when making purchases for resale or if I need to hide the piece in the back corner of the safe.
I didn't put specific names in sections, because they will be different for everyone depending on taste and funds available. It will give you a general idea of where to be. Over time you will find the pieces you really like and just become a expert on those.
Its similar to asking what is the best US/World coin to collect? I look at short term profits and long term potential over 100's of years. Depends on what your goal is.
Some will say pennies are the best series to collect and some want the more difficult private rare gold pieces to collect.
If you aren't sure on your purchase, you should be "buying the book first" or asking your more experienced peers.
A rule of thumb would be to stack the earliest pieces you can afford, funded on precious metals. If you can't afford it, look at newer pieces that are funded, rare and on precious metals, because in 10 years, a lot of them will merge with the unaffordable pieces now. When the majority moves in one direction in a market, I usually move in the opposite direction. Most people are to emotional for that though.
Yes, The lines will be blurred between a lot of the different sections. Pieces that dont have enough BTC to even be redeemed are probably treated more like BF pieces or just art.
If I had to put one at the top, I'd say the 1 oz gold 1000 BTC Cas Round or the funded Cas Bar.