Rarity Vs. Condition

And that is exactly what I'd tell that person.

I think historical rarity with provenance pedigree is the way to go for a blue chip single coin investment imho ...but not cheap

This.

The thing is that I will never benefit from any price increase. All of my coins are for keeps.

It's an interesting question. I do try to keep an eye on "resale value" when buying - even though that is rarely my first priority. Coins are not a great investment overall, IMO, but they are a hobby that can "pay back" some over time if needed. It is like gambling a bit. If one considers the "losses" as "entertainment expense" it is far more palatable than thinking of it as something you expect to win at. So depreciation could be looked at very similarly in coins. In line with what Tom said above about buying what you like and can enjoy regardless! I haven't been at it that long, but so far any slabbed coin I've wanted to sell ( upgraded from ) has brought me at least break-even on selling. I hope it stays that way but realize it may not!

I admit that I prefer a coin with a higher grade and/or "eye pop" over one that is rarer but highly worn or dull looking. I love my 62FH Standing Liberty quarter with dazzling luster far more than a dull or black-toned 66FH as far as looking at it and that it stands out(shines above all others) in my "slab" album.

I also find myself gravitating to certain details of a coin type that RedBook or others don't emphasize as much as others. For instance, on buffs I look at the liberty on the obv as much as I do the date, horn, tail, etc. Many have very weak strike in that area that I think detracts as much as the date and horn and tail weakness issues. I also look at the upper body details on the buff/rev more than most, IMO.

So what attracts some folks - and affects desirability - can vary from person to person. Luster and "blast white" mean more to me than many and others go crazy over rainbow toning which doesn't really do much for me.

I do like buying coins I think are "undervalued" compared to their population/rarity and others of that type. Makes me "guess" they will come up eventually to be more in line with their rarity. But then I am waiting on silver to get up to $60/ounce to dump the rest of my junk/bullion I inherited. LOL Could be a long wait!

It depends on the coin

Rather than settle on a grade, I'd rather do this by price. A really nice example of a much needed coin by collectors is almost always guaranteed to go up in value, take for example a nice Fine condition Chain Cent or an AU Gobrecht dollar, both have always and should continue to go up in value. Next best would be a key date in a popular series like Lincoln cents - get the best grade you can afford in a 1090-S vdb, 1914-D, 1922 Plain, 1955 DDO. Mercury dime 1916-D, 1901-S Barber quarter, etc. and make sure it's PCGS or NGC certified just to guarantee liquidity.