Let not statistics and trends be your master but, instead, be your servant. Ignore at your peril, but don't forget to leave room for intuition, insight and form study. 
The Grand National may seem, to the uninitiated, a lottery, but for long periods in its history it creates fairly predictable themes, meandering only slowly towards new trends, all of which the keen punter has to identify and interpret.
History tells us, not with absolute certainty, that the winner will probably be aged 9, 10 or 11 years old. For many years, keenly fancied contenders have fallen by the wayside due to their lack of maturity. 2015 will, I'm sure, be no different with leading contenders - Unioniste | Shutthefrontdoor | Many Clouds |  Cause Of Causes | Ballycasey | Sam Winner | The Druid's Nephew | Spring Heeled | probably failing on this vital statistic. I am prepared to take this overwhelming position at face value despite the depth of quality indicated by the list above.
The old adage of "back a 2 and a half miler" is almost certainly now completely discredited, ever more so now the fences are fundamentally easier meaning that, in a big field, they are taken along at high speed demanding tactical speed in the first 2 to 3 miles and stamina to burn in the final third. Tactical speed is a component of class. History tells us that to win a Grand National, entrants probably must have won a Class 2 (or higher class) race over a minimum trip of 25 furlongs and preferably further. Be very aware of previous success in the Scottish National (significant recently), the Irish National (highly significant in the past), the Welsh National (also highly significant in the past) and the Midlands National. I'm also very mindful of Newbury's Hennessy Gold Cup form; without doubt, to my mind, the most vital piece of staying chase form every season, though not perhaps as relevant over this extreme trip.
The Grand National throws up a regular supply of race specialists; such as Hedgehunter and Cappa Bleu. Perversely though, the contest is rarely won by a competitor which has failed previously in the race; Like all common trends, profiles and statistics, such factors are there to be overcome and occasionally, as in normal life, this happens. Mon Mome did so and so did the laudable Hedgehunter. I prefer to examine those with good form experience of Aintree but, nonetheless, debuting in the race.
There is a key BHA Rating range - essentially now between 139 and 148 and, at least for the time being, don't expect the winner to carry more than 11 stone 5 pounds to victory, probably less. 
Other key factors are a minimum or thereabouts of 10 chase starts, a minimum of 3 chase victories (preferably 2 of which were at trips of more than 25-furlongs) and, from my own study, to have achieved a Racing Post Rating (very reliable) of at least 150 in a steeplechase.
In recent times, I've given less credence in my weighting of factors for selection purposes, to trends, except in this race. It is unique, being over a trip far in excess of the distances usually travelled by its competitors, at a time when the ground is changing as winter turns into summer, with the biggest single field coming under orders at any time of the year. 
Taking all of these factors into account, one horse stands out meeting every criteria and warranting maximum support and I've a case to make for another to win and 3 others, at bigger prices, to place. Alongside this theory, I've no doubt that at least one previous runner in the race will again perform with credit but probably not win i.e. I suspect Rocky Creek (5th last year) will again be competitive and just fall short - his stamina seeping away in the final stages and Alvarado may creep a little closer and be the latest perennial bridesmaid. 
Please wait until the day to place your each way bets as at least one bookie will offer 7 places and others, 6. 
One other notable factor for the National is the application of headgear. Worn ever more prevalently and by better horses more regularly, the National is, perhaps somewhat surprisingly, different. In the last 4 years, of the top 6 finishers each time, only Double Seven and Chance Du Roy did so, and that was last year. Of the last 4 winners, I can't find that any one of them wore headgear in any race during their entire career - not even a tongue tie to aid breathing.Perhaps the reason for this the big field and the importance of having a broad vision of what's going on around the horse. I guess breathing has to be spot-on too for such a mega distance. Just a thought.

My selections are:

To Win - Godsmejudge (Best) and Al Co (Next Best)
To Place (not each way) - Carlito Brigante, Wyck Hill and Portrait King
Each Way (provided first 6 or 7) - Rocky Creek and Alvarado