I'll give you a BIFL answer that's not super heavy on performance. I'll assume your primary goal is commuting or some light exercise.
- Stay away from carbon fibre. Stick to aluminium or better yet, steel.
- Choose a bike that has a fanbase. For example Bromptons or Surlys are expensive for what they are but you can maintain them for a lifetime.
- Stay away from the cheapest bikes. If you're going for a low budget bike try to stick with a mainstream reputed bike brand like Giant.
- A belt drive is more hassle free if you have the budget.