I'm assuming you are being forced to choose a narrower focus due to resource constraints. If not, there is no rule that says you can't grow both simultaneously.

If you need to initially focus on one segment then start by evaluating your position in the market. That means identifying the best opportunity to position against competitors and find a niche. Also, providing a solution customers value at the price point that is profitable is vital. Is there long-term value where a symbiotic relationship can be developed versus short-term income where new customers need to continually be acquired? These are some of the things you need to consider when narrowing the scope of your offerings. The best way to evaluate is create a comparison chart and rate the two services against each to help in your decision making. Once you make the decision go all in!