I'd say a 4.8 would leave you underwhelmed for the work, a 5.3 would be a nice pick-up from the stock engine, and a 6.0 would give it good feel but start to impact MPG's if that is a concern, although I don't think any of those would get you lower than stock MPG's. As far as ease of fixing and parts availability, I think the scales are tipping towards the LS stuff. It's getting harder to find SBC stuff in stock, and even harder to find people who can work on it. LS parts benefit from the 50 years of the SBC plus computer design and modern engineering. When you get rid of the EVAP system and some of the other stuff, you are left with a very solid and reliable platform that can generally notify you of an issue before you would generally know it yourself, often diagnose itself, and is generally easier to repair if you are coming at it from a blank slate. 90% of anything you have to do that doesn't involve internal repair can be done with an 8mm, 10mm, and 15mm socket, a screwdriver, and a pair of pliers. On top of that, gaskets are generally reusable with no sealant needed. If I have the choice of replacing an intake on an SBC vs an LS, there's no question which is easier.
Yes, EFI pumps suck to replace, but put a good one in the tank and wire it up correctly and you shouldn't have to mess with it in the next decade or so, even with heavy use. It's one of those things that a mechanical fuel pump is easier to change, but you are going to have to do it more often. And if you are super worried about it, make an access plate over the sending unit, then you can change it out whenever you need just by pulling back the carpet.
