Depends on your long term goals and which one is most important. Meaning, do you need something mild now and something to build onto later for big power?
If you're able to go with a straight 5.3 with some boost, it's hard to beat it for the money and reliability. Especially if you're still working with stock drivetrain parts. The 4l60e won't cut it for much for the 500WHP unless it's a built unit. But a 400/4l80trans will work well now and later for big power. They're both fairly easy to put in. Especially the 400. You'll be needing some good axles/stubs and DS as well. And they're not cheap, but will be needed at some point.
I'm assuming you're looking for the best bang for buck with your thoughts set on running fast ETs at the track. (Like most of us)
The 5.3 is hard to beat for the money. (Gen 4 preferred) There's so much information here for support, too.
a big bore/stroke 6.0 is a great foundation for both now and later. It will give you a great foundation for a powerful N/A build right now. But again, if you're going to add a power adder to it, you'll be slightly limited as you'll want to install a decent Heads/Cam/compression combo on your N/A motor. But, these parts are expensive and don't always match up well between the two very different setups. Finding the right combo that will work well between the two is key. If you have E85 where you live, you have a bit more forgiveness. (Wish we had it here
All of these engines drop right in with minor changes to things like the front timing cover, valley cover, Cam extension harness/Knock sensor harness and possibly a hole drilled into the front of the block for your Alternator that's needed for 05+blocks. If you get an engine with a 58 tooth reluctor, you can purchase the conversion box for another cost.
If I were you, I'd look into some of the vendors here and check out there short/long block combo's. They can spec you out a shortblock, cam and heads that will work well for both N/A and Boosted setups in either Gen block you need.
Hope this helps a little.