The reason I ask is because it depends on how large his portfolio is already. For instance if he has 1 million invested and he just sold one of his positions. Then it wouldn't be a bad idea finding a particular company he thinks will grow in the next couple of years and throw his 50k into that stock. Or if he thinks a particular sector will grow over the next couple of years then find an ETF that mirrors it and throw that 50k into that. Depending on the stock/sector I would most likely dollar cost average into it.
Now lets say most of ones money is in cash/real estate/etc. and this 50k is going to be the only stock investment. I personally, wouldn't throw it all into one stock. I would pick 10+ stocks/etfs/etc. and dollar cost average into those positions.