What wood joint can I use to connect railing members over a post?
You have a couple things going on here, so let's clarify:


There's no joint that makes anything "stronger" here if you're using adequately-sized railings and appropriate fasteners to begin with. You don't need the rail boards linked together in tension. It's not important. Railings don't fail by falling off the post along the rail assembly. If they fail, it's due to the lumber cracking or getting pushed off the fasteners somehow. 
Therefore, it's entirely a matter of aesthetics. How do you want it to look from the most common perspective?
The main point of using something other than a square butt joint is so that, after the railings shrink, you don't see the resulting gap as readily. A bevel joint hides the gap visually. This applies to decking, siding, and any other joint in wood. A half-lap requires substantially more effort, but allows you to use fewer fasteners, which has both cost and visual benefits. 
You can make things weaker with the wrong approach. The half-lap as you drew it in your previous question will weaken the railing, because you've halved the thickness of the boards all the way to the edge of the post. If you imagine a cartoon dumbbell sitting on the railing just beyond the right edge of the post, all the weight is being supported by half the railing's thickness if we assume that it'll easily split lengthwise along the grain. Bad news. 


If you're bent on a half-lap joint, the solution is to make a narrower connection, such that it's just wide enough to securely fasten it to the post, but doesn't compromise the strength of the board at or beyond the width of the post. 1-1/2 or 2 inches would do nicely.

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