Be realistic about your choice. A waifu or husbando should foremost have [personality] traits and [moral] standards compatible with your own (self-awareness can ease the selection process). By standard definition, this represents a character you would enjoy being together with. For example:
- If you prefer courage and empathy, consider a Tsundere.
- If you desire passion and loyalty, consider a Yandere.
- If you value grace and modesty, consider a Nadeshiko.
Also, it is important to acknowledge character flaws as well as strengths. Although I defined each using their good points, Tsundere can act violently temperamental, Yandere can be psychotically obsessive, and Nadeshiko can prove unintentionally boring. Note that I use these 3 templates purely to illustrate my point (your candidates likely differ). Finally, not all anime characters conform to archetypal ideals, which may complicate your decision-making.
I must be very bored right now.