If this was a choice I was making for my car, I would run two equal length and gauge wires to each sub, especially if the subs share a common air space. As long as you are using the appropriate size wire for your power and length of wire runs, both option will work.
BUT, if the wire is undersized for the power or length of run, the second sub could receive slightly less power, and with a common air space, the cone excursion from the first sub receiving more power could rob cone excursion from the second sub, slightly softening the overall bass hits.[/QUOTE]
That's simply not true. Where you getting your info from? If I had a 3 ft long piece of spkr wire going to my amp from sub, and the other speaker wire was a foot longer, also going to amp from sub, your not gonna hear a difference, nor will the other sub have more bass than the other....or even less power.
Thinking outside the realm of an informed car audio enthusiast here. Since the OP didn't state the power of the amp, the length of wires he running, or the wire gauge being used, let's assume the worst in that the OP might be using 15-feet of 20-awg wire, pushing 1000-watts, and worse, left an entire 25ft spool of wire laying inside the box running to the second sub because he didn't know better. If you've worked on or been around long enough, you'd be amazed what people will do.
I don't assume that all knowledge is common, and there are newbies trying this stuff out everyday. Based on the OP's core question alone, the answer was correct in that electrically, both wiring setups are the same, parallel.