The "best" is really only what you need. IMO building your own/having one built is the best because you get everything you want/need and nothing you don't and at a very reasonable price. The one I built last year would have been nearly 2x as much money from a name brand . Only downside is that it is a bit bulky and some of the features you can get on name brand machines you can't get on the custom ones. If you just want a serious machine to do some serious work that doesn't really matter though. 

The first thing to decide is do you want a laptop or portable computer? Mine is a 17", very thick, very heavy, battery sucks, it really makes for a terrible laptop but I just wanted something portable enough to go between desks really.  The new laptops are extremely thin and light which makes them nice to use as a true laptop.

I'm guessing your FIL does not need much for speed, power or memory so that really keeps the price low. If you don't need much of that stuff IMO it's not worth building one, just go find one at the store thats easy to hold onto and use. Since you have to help him, get something thats easy for you to use too.

I don't think either brand is better or worse simply because of the brand. Each has good and bad models. The good news is that every person across the country buys laptops so finding reviews on them is a piece of cake. Make sure to search specific model numbers, one little number can make a big difference.

If at all possible, get him Windows 7. Not sure how it works in the stores, but I was able to order mine with Windows 7 for a small fee. It's worth every penny IMO and will be easier for him to understand. I'm not very old at all and find my way around computers just fine but still think somebody went off the deep end at Windows with their phone OS and Windows 8.