I'm a whole food omnivore at the moment. Considering juicing, vegan, vegetarian, pescitarian etc. What, how And why should I eat.
There are two primary aspects to a good diet in my opinion. These are:
1. Health considerations and
2. Moral considerations.
Satisfying both of these will help you have the best diet possible.
Health concerns will be more quantitative, and in some respects relatively universal. Things like a nutritious and balanced diet sourcing a range of foods, calorie control relative to your level of physical activity, avoidance of any intolerances/allergies, avoidance of excess, or overly processed foods that can often contain far too much salt, or other undesirable additives.
Ive always had a rule of thumb, if you're food is colourful you're on the right track, if its all 'beige' your not eating right.
In keeping with that i think part of a healthy diet is having a good relationship with your food. That by cooking yourself from raw ingredients as often as possible will ensure quality, free from additives, be cheaper than buying ready-made foods, and will also be more fulfilling and satisfying having made the food yourself. Taking it to the next level and growing some food will also do this.
From a moral perspective, this is a little bit more qualitative, and ultimately individual. I for example, when pushed to really think about it, cannot justify eating meat under standard everyday conditions, where you buy it in the supermarket without any emotional engagement. That it fuels a ruthless meat industry that on a daily basis utterly obliterates animal rights on a genocidal scale.
This is something you have a duty to yourself to look into and then make an informed decision as to where you draw the ethical lines, and what sorts of behaviour you feel you can support or oppose.