Choosing Between Mindfulness and Compassion Meditation

My limited knowledge about compassion meditation is that it does/can generate some type of meditative concentration. Here is a little explanation of compassion meditation: http://www.oprah.com/spirit/compassion-meditation

Mindfulness gradually grows awareness(which leads to more tranquilty in a person but only after attaining high enlightenment stages it becomes permanent) and during the path it temporarily generates mind states with high awareness too.

For the first question, I think this part of the video(6:40-7:38) can be helpful: https://www.youtube.com/watch?v=GDDY4gOexVA&feature=youtu.be&t=400

Mindfulness is the only way to gain insight, purify the mind and achieve enlightenment. If you wish you can mix your mindfulness practise with Samatha, compassion meditation or other types of meditation, but at the end only mindfulness leads a person to complete and permanent freedom from suffering.

But ofcourse it is up to the person to decide which path is more suitable for him/her.

To keep it short and simple (This is worth elaborating on):

Metta bhavana is meant for ameliorating dvesha (avsersion towards different people, or yourself).

Vipassana has multiple purposes, one of them you've already mentioned: to develop concentration. There are other purposes as well.

Not sure if it helps, but a different approach is to find a clear understanding of the problem. What type of dukkha/tanha/upadana are you looking to manage? Are you suffering from moha/raga/dvesha? Et c. Exploring these things might guide you in how to practice your meditation.

Ideally one would contemplate to rouse motivation, make effort in developing good qualities and become glad on that account.

Metta and Compassion just as Appreciation and Rejoycing can be used to rouse gladness and to establish these perspectives due to frequent giving of attention.

Therefore any amount of time dedicated to development of perceptions is great.

If one is dilligent in giving attention to these themes which are fit for reflection, one can be expected to develop good behavior and see lights & visions.

Also pondering the themes reveals the elements as one eventually 'sees the point' that is the element, as a referable factor coming into play that can be shown to be a truth of the world.

However developing concentration that leads to mindfulness & alertness is necessary to be able to maintain skillful perceptions.

So is development of pleasant abidings necessary for contentment.

Ideally one would contemplate to keep focused on developing mindfulness and the pleasant abidings.

Failing to do so one dwells in pain and is one with a painful practice; without a pleasant abiding.

If you want to develop mindfulness more that is ok if you aren't particularly cruel to yourself and others, it's impossible to tell just how cruel one is until it's (compassion) development culminates.

In so far as your quesstion is about Meditation, I cannot say anything. But if you were to mean Buddhist meditation, then I can say the following- The meditation technique which Buddha taught, which is the teaching of the Buddha and the basis for all philosophical schools, is Vipassana. Other techniques serve as efficient and helpful techniques, depending on the individual. So for example, if someone is unable to meditate because they cannot concentrate their mind, they would be suggested some technique (like anapana or samatha {which in fact is considered as a pre-requisite for Vipassana by many schools}) or a skill in daily life (such as reciting a particular mantra or counting the number of beads in a mala) that would develop some concetration, which will allow them to practice vipassana. Or if a person were too obsessed with physical beauty, with lust- so much so that they cannot practice vipassana, they would be advised to meditate near the dead bodies.

Vipassana involves not only the establishing of the four-fold awareness and the insight gained from it, but also leads to one becoming more compassionate and more aware (mind-fullness). What I mean to say is that, the two aspects you have asked about, comapssion and mind-fullness are not seperate- they go hand in hand- one helps in developing the other which helps in developing the first. But it is possible that one may have some problem in developing mind-fullness or practicing compasssion. Therefore, in such cases, as per the understanding of the teacher (spiritual guide, elder monk) certain technique of meditation (like verbalization or visualization) which is not Vipassana, would be suggested in that particular case, so that the meditator can continue making progress.

Only you would know where you are in your progress and only you would know what problem you have with regards to you meditative practice. I suggest you read further literature so that you can understand in your own way of thinking and continue practicing. Do not get involved with questions to the extent that you stop meditating at all. Neither ignore the questions that have occurred to you- and if you cannot answer them, then consult a senior monk, or your guide.