The Most Promising Coins

It seems everything is overpriced these days.
That said, I think that American and European coins may underperform. Demographics of the US and Europe will be the main cause of that.
Perhaps coins from South America or Africa are still good buys?

The platinum Russian 3, 6 and 12 Roubles will always command collector attention, and thus be a good investment on World numismatic market.
They are historically significant, the 3 Roubles being the only platinum coin that entered circulation.

Novodels are always scarce, but be aware of copies.

Korean and Japanese dollar sized coins in MS condition always find good prices at numismatic auctions.

Be aware of Chinese fakes of Chinese silver coins, but the genuine have a good future in Chinese and World coin numismatic auctions.

My buying technique for World coins is to always look for best value for money at the time of purchase, across the whole of numismatics, including hammered milled and ancients.
I am a generalist, not a specialist, and definitely not a set builder. Concentrate on the key hard to get coins only, because that is what all collectors are on the lookout for. I leave the more common coins for other collectors.

Condition by itself not of primary importance, but condition versus value for money certainly is.

From my experience, acquiring coins in the $50 to $100 value range certainly works well with this approach. That is the value range per coin for perhaps more than 50% of my collection, and I have been collecting coins with this approach for most of my numismatic life. I am an old guy these days.

Before comitting to buy any coin, do your due diligence research knowledge and price research first, to give yourself the best chance of finding a numismatic bargain. That is much easier to do, when searching across the whole of numismatics. It also heightens the need to do lots of knowledge research for any particular coin that you may be interested in.
That way, you give yourself the best chance of buying well.

Curiously, I have only a weak investment motive, but in the long term, I have done reasonably well.

I collect across the whole of numismatics.
Because of this my knowledge in any specialist area is much less than it need to be to make good buying decisions.

For example, if I am interested in an ancient Roman sestertius of Hadrian I will search site Wildwinds to increase what I already know about these coins. I will also search Vcoins for pricing information as well as Google images on similar Roman sestertii for sale looking for similar coins in similar condition. and auction records for similar coins.
If everything lines up, and the coin I am interested in appears to be excellent value for money, I will seriously consider to buy the coin in question.

Lots of work perhaps, but if your interest is in numismatics, the work becomes good fun.

To open up the possibility of finding numismatic bargains I will investigate obvious opportunities across all coin collecting areas.

I have about 200 books on numismatics generally and I will search all appropriate book references.

That sort of research process can equally apply to modern World coins renaissance coins Islamic coins, Byzantine Chinese, or coins of the Indian sub continent over the last 2,200 years.

To help learn as much as I can, membership of the CCF is a significant factor, because I have lots to learn from other members with specialist numismatic interests.

sel_69l, you have a very good coin buying strategy. Thank you for mentioning several sources of your search for information about coins. Can you recommend other sources to search for modern coins?
As far as I understand, you specialize in antique coins, judging by your avatar.
Sometimes I browse ebay to find attractive coins (outside of my specialization, although I don't have one as such, there are only preferences) that will brighten up and diversify my collection.
I am still searching for a certified coin of ancient Rome, as well as a medieval European coin. I want to have at least 1 example of coins of this period of the history of coinage.

For modern coins in particular, I have Krause World Coins for picture reference:
1900-2000,
1800-1900,
1700-1800,
1600-1700,
Krause World Crowns,
Coincraft's Srandard Catalgue of English and UK coins (about 700 pages)
the Red Book for U.S. coins,
on-line reference NGC World Coin Values,
Current auction records on line for World Coins (Noble Numismatics Australian they auction about $10million in general numismatics per year)
Euro Munzencatalog - (Euro coins)
Swiss Coin Catalog 1798-2008
Commemorative Coins of Modern Sports
Standard Catalog of Mexican Paper of Coins Paper money and Medals
Coins, Medals and Tokens of the Philippines
British tokens and Their Values
Rennicks Australian coin and Banknote Values.
(This list incomplete)

Google Images for particular coins
Google any particular coin

The above references are modtly out of date price-wise, and so it is necessary to research current and recent auction and ebay records.
When considering to buy a coin, price research often takes more than 50% of the research effort - so lots of keyboard time is spent.

I also have an extensive library on coin forgery, and how to identify fakes and metallurgical references and testing to aid the identification of fakes. Keyboard research often useful in this regard as well.

I still collect current Australian commemorative coinage, taken from pocket change at face value - have done so since 1966, when Australia converted to decimal currency.

First follow your heart. If you like it enough to collect it for a long term and you are will to research it, publish it and exhibit it then it will usually prove to have been a good investment. Helpful factors would be a healthy growing economy in the country of issue. Good serious designs that are meaningful to the country of issue. Avoid childish cartoon designs from a country that doesn't have it's own mint and does not grant legal tender status to coins issued in it's name.