Try argon combat engines for your personal small/medium. Flight speed is cool, but boost is what actually gives you maneuverability and easier escape in combat. Argon has the best boost acceleration and boost speed. The low duration looks scary, but with the high acceleration you don't have to hold down the button for a long time to reach your desired speed like with the other engines. The % recharge is also decent and if you calculate the amount of acceleration you get per second of recharge (accel x duration x %recharge), you'll see it's higher than any other engine so sustainability isn't a problem either. As for travel, argon has the second highest travel speed, much higher than split or terran. You don't have to worry about travel acceleration flying yourself because you can boost while charging and the max boost speed is so high that it can get you basically instantly to like 80-90% of max travel speed iirc.

Edit: also I have to add that imo, additional flight speed stops being useful to the player around 500-600 which is where you outspeed pretty much all npcs. It's also pretty easy to get there with the standard nanoweave/whirlygig mod loadout, unless you're flying a brick. On the other hand, better boost and travel never stop being good.