No one really makes "straight" feed lips. The "classic" style is tapered. There are a few knock-off magazines with near-straight magazine lips, and also the WWII era Ballester Molina magazines have near-straight lips (excellent magazines, by the way - real old-time construction with pinned bases and sturdy steel bodies). Most modern factory/OEM magazines nowadays are made with "hybrid" feed lips that are tapered the first 1/2 of the length, then open up slightly but not as abruptly as the wadcutter style. Many aftermarket magazines are wadcutter style with really abrupt releases and are designed to overcome variations in ammo and gun specs.
I have had almost every major magazine brand and type through my hands over the last ten years and tried them in multiple guns - Colts, Caspians, a Norinco, etc. The best operating magazines I have found on average are true-blue, basic Colt brand 7rnd. magazines. I prefer them even over the more expensive "boutique" offerings from Baer, Wilson, and Tripp. The Colt magazines are manufactured mostly by checkmate industries and also by Metalform. Colt is usually the cheaper source for them if buying new.
I also have great success with real "GI" mags - I have about 10 or so WWI era and WWII era Colt and various GI subcontractor magazines, and they all work great, too. Even with HP and 200gr. LSWC rounds. However, no one really makes these magazines anymore.
Keep in mind, if there's a kink in your gun - a miscut ramp, a catch hole not in spec., a mis-cut or over-zealously modified ramp - your gun can be finicky and unreliable even with excellent magazines. My rule is that if a gun doesn't work well with vintage GI or Colt brand magazines, then I figure out what's wrong with the gun, not attribute it to magazines.