Metta and Vipassana Meditation
If one wants to be totally free from all sufferings one will have to practise vipassana insight meditation. This is because the objects of Brahma Vihara have beings, a concept, as its object. To gain wisdom that reaches beyond birth and death one has to see into things as they really are, i.e. realities.
But if one has developed Metta or other Brahma Viharas then one stands at an advantage. The mind can concentrate easily. Once the mind is calm, one can emerge to do the work of mindful observation of the mind and body processes. It can help us overcome tiredness and stress of watching a lot of pain. One who does insight after establishing oneself in Metta Bhavana first is called Samatha yanika, i.e. one who makes tranquillity as one's vehicle.
One may also develop Metta after one has begun insight cultivation or one may even do it hand in hand. But usually because of lack of time and need for concentrated effort, one of them is done first to some degree of accomplishment to serve as a support for the other.
Where Metta serves as a support for the complete cutting away of all defilements to win freedom from Samsara, then Metta is at its noblest. Often one may be at a loss as to which to practise first or how to combine or when to do it.
Usually I would advise that one first attends at least a period of vipassana retreat. This would enable one firstly to get a grasp of the most essential part of Buddhist meditation the way out of samsara, at least at the basics. Secondly one also gets to learn about and how to use the all-important factor of mind control-mindfulness.
Then one can proceed to learn the basic method of developing loving kindness. It is best to go for a retreat to develop deep concentration and get a real feel of it. Then one can learn to combine the two. It is important that we get a thorough grasp of the method. To do that it is best that we put whole-hearted effort into learning one method first. In trying to combine the two we have to be decisive as to when to practise which one.
For example, one may decide to do fifteen minutes of Metta, then followed by vipassana. Then one may feel that, before the time is up, the vipassana objects are becoming very clear and so one is tempted to switch. Or one's Metta may make one feel so good that one is in a dilemma whether or not to switch. A decisive action should put away all these conflicts. A decisive action also ought to be founded on wisdom.
If we want a full session of Metta, then we may use the morning sessions for Metta and the evening for Vipassana, or vice versa. It is not wise to forsake any one, for both are important.
One may devote more Metta in the case where one's life involves dealings with lots of people. It may also necessitate more time for Metta if one's temperament is prone to ill-will and bad temper.
A suitable balance can be drawn up when you sit down to consider what you want and what is good for you.