I liked the braided -AN lines with no hassle of bending the lines. Very simple. Did enough of that with the fuel lines from the tank and the brake lines.
It's all personal preference. If you can go either way and don't have a pre-bent fuel line and you are not very confidant about bending them, then a flex setup may be the way to go.
It may not be stock but being it will have a stock type mechanical pump I would run a hard line so it looked stock. Unless you are going after the non-stock look then use a braided line. I like the hard line because it can be bent and shaped to fit around or behind things like alternators and brackets.
I like the clean look of steel (or SS Steel) lines with AN fittings. I'm just learning how to bend them. I used 3/8ths steel tubing from the local chain parts store and AN -6 fittings. To shine them up a little I used green scotch pads to buff them.
My build mentor showed me how to use the bender and flare tool. This is my first attempt. Came out right the first time!!! I'm SURE that will never happen again. To keep them from rusting I'll shoot some clear coat on them. Eventually will redux them in ss steel.
One problem is that the AN fittings (and braided hose if you go that route) gets expensive FAST. I was surprised how fast it added up.
One thing I do like is that I bought some Earl's AN -6 plugs and caps to plug the lines when I pull the carb off for maintenance. Maybe over kill, but for a few dollars (the cheapest of the fittings I bought) I can keep the fuel from continuing to leak and keep the debris out.