the valve racket from flat tappet cam & lifters is quite different from that of solid roller tappet & cam combo. If that matter to you then the prudent course would be to listen to both before coming to a decision.
I confess to being prejudice in favor of the flat tappets and cam, as most of my old Ford experience is with the HiPo 289 K code engine. But I've never been sidelined with a cam or lifter issue, and but have had the great pleasure of passing a few cars that were DNF due to disintegrating roller lifters. They take a beating, especially in a street car where inevitably there is a lot of low rpm use. If you are willing to change them out on a regular basis, then no problem. Otherwise watch out, especially if your car is going to see considerable action.
So here's one vote for solid flat tappets. I put over 50,000 miles on my last car, a '66 GT350 with a vintage Paxton and original 289 motor. Most of that milage was just normal "spirited" driving, but on numerous occasions I had the opportunity to run flat out for as long as full tank of gas would allow. No engine issues of any kind. I had a Melling high volume
oil pump and was using Mobil 1 15w-50
synthetic oil, and of course a stock Ford HiPo flat tappet cam.
Z.