This game starts with $6 million on startup, doesn't it? I'm talking about 3 (actually 4) MD-8x on startup. Or 6 737-200s. Yep, neither is fuel efficient. But the leases are cheap for the number of seats, and they are available. That's basically all that's there in the 100-200 seat range currently. The others in that group are Avros & 717s, which are equally inefficient on fuel, and cost far more to lease, and the BAe 146 & 737-3/4/5. Those are probably workable too, but there are less available.
If you want to go bigger, there are a300s and L1011s there, but they are really old, plenty thirsty, and you don't have too many routes out of Bradley for them. Can still be done though, I started my airline a few years in with 2 a300s, and grabbed more a300s & CRJs whenever I could get a loan for more. I'm now 2 years old, and am about to start phasing out the a300s.
If you want to go smaller, there are plenty of dash-8s, An-140 & F50s there. Very fuel efficient, but slot costs will mount quickly. Personally, if I was starting in Bradley, I'd go for 4 MD-8x, and then grab more of them and one of those 3 props whenever cash was available.
Why write 'but apparently they have horrible fuel burn stats'? Why not look up what the fuel burn is? MD81 burns 22.5kg per pax per hour. 737-200 26kg, 737-5 21.25kg
As for your turnarounds always being less than 5%, you only had 1 plane, so it was very easy to see exactly what your routes are. Since you've just restarted, I can't actually quote them.
But your late night flight to Detroit had a 45 minute turnaround, which is well over 5%. Your new schedule has 65 minute turns each and every time, which is 1.4%. So no worries.
So, I've now got a few questions for you. If there's a good reason, please explain it. If there's no good reason, think whether there's a good reason to change. Currently, you're running at 1.4% chance of delay on every turnaround, yet you have a 4 hour gap from the end of your detroit flight to the start of your Atlanta flight. Why not make the turns for those 3 flights 70 minutes, and reduce the chance of delay to the minimum 1%?
Your 2nd plane has 2 flights and a 7hr, 20 min gap. A round trip to Atlanta takes 7 hr 25. If you put a 60 min, 8% delay chance turn in the middle, it takes 7.20, and so fits perfectly. If you don't want to use an 8% turn, why aren't you flying a slightly shorter route instead? There are multiple empty routes available.
You've chosen 3 routes: Orlando can handle 10+ flights per day, and takes 8.20. Atlanta 10+, has 6 competitor's flights already, and takes 7.25, or 7.35 with 1% turns. Detroit can handle 2 flights, and has 2 competitor's flights already. The competitor has an ATR, so will likely increase that to 4 daily flights. 2 Atlanta flights leaves a 9.10 gap for the third flight, more than enough for another Orlando trip. Why are you flying to Detroit? Why fly twice to Atlanta and twice to Orlando instead of 4 times to Orlando?
A quick look at route planning says that along with the empty Orlando route, there's an empty route to Nashville (1-2 planes, just under 7.20 round trip), Chicago (10 planes, under 7.20, and the competition flies 2 jumbos a day), Indy (empty, 1 plane), Midway (empty, 1-2 planes). If your first 5 planes go twice daily to Orlando, once to Chicago, then the next one 3 x daily to Chicago, when the 7th plane arrives you'll be able to set up a 7 day schedule to just those 2 airports, flying 10-11 times daily, and fill both routes.