This rickety subject of timing didn't come out of my head, oh no, it was all my Twitter followers' doing who asked me to write about it. But, however, because they know me better than I do, as soon as they asked, I realized I did both and have perhaps something to say on the subject (whether or not it will be a wise thing, I doubt it). Anyway... How do you choose what tense to squeeze your story into? I say, don't. I say, the story will tell you itself and if you try to bend your story, it will bite you back, so I highly recommend to steer clear of it, that is, if you want your story to have teeth, of course. Let me just recount my personal experiences on doing both and you decide for yourself what suits you best.
Present tense is more personal. When I started writing SIREN SUICIDES, I didn't think about it in terms of a novel, it was more like therapy for me, to let out my personal pain, to bleed it out on the page and feel better. Naturally, most sentences started with words like "I feel nothing..." and "I hug my hunger..." and such. It was as if I was writing about me, only it was Ailen Bright speaking, my character, speaking through me, yet allowing me to be very much in touch with her, as if possessing her and re-experiencing everything through her eyes. It felt very personal, it was hard to write, but it was also very cleansing. So I would suggest, if you are ready to see your story unfold through the eyes of your main character, choose present tense. But, remember, you will be restricted by only being able to cover what the character sees, without being able to shift between characters.
Past tense is more observant. Now that I'm done with SIREN SUICIDES and am writing ROSEHEAD, I'm gleefully enjoying writing in the past tense. Why? Because it gives me the status of on observer. Where as before I was being able to look at the world from one perspective only, literally, looking only through Ailen's eyes, now all of a sudden I get to soar above the world I'm creating, shifting between scenes and characters and places at will and sensing more freedom, yet at the same time a bit less of a personal connection. Is this a good thing? Yes, I let the story drive me forward, unlike I did with SIREN SUICIDES (I meticulously plotted it and am writing ROSEHEAD without any plot whatsoever). Is this a bad thing? Yes, I don't feel as personally connected to my main character. But, on the flip side, I am able to connect to more characters and develop them better, because I am slipping in and out of their multiple skins. So, does it let me develop an overall richer background? You bet, for one, as compared to only 8 characters in SIREN SUICIDES, I have a whooping 26 and more coming in ROSEHEAD. Compare Life of Pi and A Game of Thrones, you'll see what I mean. Both are excellent and very different.
Past tense is more complex, present is simpler. I am, of course, grossly dumbing down the concept here, but it's only because in this blog post alone I won't be able to demonstrate the difference, but if you could just go to Amazon right now and read the beginning of Fight Club and 1Q84, for example, you will see how one grabs you personally, and the other grabs you observantly. I'm by no means an expert, but it felt to me like this when reading both novels, and I'm sure that scores of you will disagree with me. Again, this is my first time writing novels, so I can't tell you with an important look in my eyes and my chest puffed out like that of a popinjay that I'm absolutely right, but I'm an avid reader, and that's the impression I get. If you set out to create a complex magical world, chances are, you would be better off with past tense. If you are wanting to write a highly emotional personal novel where personal experiences are core to your character, it's probably better to choose present tense.
The takeaway from this? Take the lead from your story. That first sentence you put on the napkin when you had your idea first surface in your head, what tense did you write it in? That first attempt at seriously starting the first chapter, what tense did you start in? Your subconscious is always smarter than you, go with your first impulse. Your first impulse is always right, yet the longer you linger, the more you will start thinking, the more doubt will settle in, and ultimately you might lose that spark that you had and feel obligated to me your piece of art, because you started, not because you feel excited. So be foolish, pick what comes naturally, and go with it. Remember, you can always write another book after this one.