Welcome to the forums.
Before going any further, it's critical to pinpoint exactly what you mean by 'investment'.
Generally speaking, if you are looking to purchase whiskies that will eventually escalate in value and/or become very difficult to procure in the future solely with an eye to being able to open and enjoy them down the road, then your range of choices is quite broad.
However, if you are planning to purchase such whiskies only
in an attempt to realize a considerable appreciation in value in terms of selling them in the future, your plan represents a far greater, and far more risky, challenge. I would caution you against taking this route, as your hard earned cash would probably be better invested in other ways.
The speculative market in 'rare' whiskies has exploded over the last decade or two, as many individuals have jumped on the bandwagon in just such an attempt to profit from their 'investments'. This phenomenon, in turn, has radically altered the 'landscape' of the 'rare whisky' segment of the market. Bottom line: With a greater number of individuals partaking in such purchases and an increased willingness on the part of distilleries and their parent companies to cater to this market with 'limited edition' releases, it has become extremely difficult to predict which whiskies will gain substantially in value and which will simply linger in the doldrums.
I'd seriously suggest you concentrate on purchasing only
whiskies you fully intend to open and drink in the future. If, by chance, some of these do dramatically increase in value down the road, you will then have the happy task of deciding whether to enjoy them yourself or to sell them to someone else.
There are many worthwhile strategies to employ in this sort of pursuit, such as concentrating on whiskies from closed distilleries, whiskies that are issued in very limited quantities or whiskies that are set to be replaced by newer versions. You may also wish to focus on the whiskies from a single distillery, thereby acquiring a number of different bottlings from said distillery - this is a good way to go, by and large.
Be aware, however, that the 'golden age' of being able to buy very fine whiskies that have since gone on to become collectors' items has, by and large, passed. In short, don't expect to find too many true bargains these days.
1. Always buy first to enjoy rather than simply to invest.
2. Buy whiskies that taste good.
3. Establish a budget, and stick to it.