Not a CS researcher but I would say that advisor is extremely important, but also within the field you are interested in. A good advisor can win you over only so much - there are people who switch advisors because of research topic reasons too (not just because they feel abused). Though if you are in the topic you want to continue in, a good advisor can make a huge, huge difference in terms of getting the most out of you and also promoting you among his /her peers.
To some extent I would not choose based on current market trends - if you want to go to grad school, you're looking at a job market many years down the road (esp. if you do a PhD). However, "saturation" is an issue and this could be demotivating. You definitely don't want to choose a boring topic. If "Bioinformatic/quantum computing" is interesting to you but you're not sure of its applicability/potential but you find it interesting enough to study, I would say this is the perfect field for you to study. Maybe a "deep learning" type revolution is around the corner - or maybe you're going to be part of making it happen.
Not to say market trends are unimportant, but as elonmollusc says, you can end up changing your field of research later - so you should some extent study what interests you most at each moment in time.
To some extent I would not choose based on current market trends - if you want to go to grad school, you're looking at a job market many years down the road (esp. if you do a PhD). However, "saturation" is an issue and this could be demotivating. You definitely don't want to choose a boring topic. If "Bioinformatic/quantum computing" is interesting to you but you're not sure of its applicability/potential but you find it interesting enough to study, I would say this is the perfect field for you to study. Maybe a "deep learning" type revolution is around the corner - or maybe you're going to be part of making it happen.
Not to say market trends are unimportant, but as elonmollusc says, you can end up changing your field of research later - so you should some extent study what interests you most at each moment in time.