To put it simply, wholesale is buying products in volume. Price is based on amount sold, so the more you order, the better price you get per item. Drop shipping you are in essence selling someone else's products, you are acting as an agent. They provide you with permission to market their product/s, then upon sale, they ship to the buyer themselves, so you don't actually ever touch the stock.
Wholesale will almost always deliver better potential profit margins, as the cash outlay means the risk is higher for the retailer, where as with drop shipping, no or very little cash is out-laid , less risk equals less profitability.
Most retail business works on a very simple formula, risk equals potential reward. The higher the risk, the more potential reward is usually on offer.
Why do I use the word potential?
There are very few guarantees in life, and even less in business. Whatever the risk size, reward is only ever potential until a transaction is 100% complete and you have the cash in your account.