Looking at your current airline, you don't have an aircraft that can operate off of the runway at your starting location.  Toronto City has a pretty short runway, the largest airliners that serves are Bombardier Q400s.  A 737-400 won't be able to operate there.

Because I think it's one of the cooler "classic" GA aircraft (ie 1960s-early 1970s), I'd go with a custom retrofitted Navion Rangemaster G/H. They have aged pretty well, since they have a strong community that has focused on keeping them in good shape, and the Rangemaster G itself was the community relaunching the aircraft in the mid 1960s after its first discontinuation (so it has what pilots wanted as opposed to what manufacturers thought pilots wanted).
 

More pics of this specific retrofit (I'd have gone with one of the more modern cockpit retrofits, see the main page of the site linked if you're wondering what that looks like: http://navion.com/N2540t.htm)

I think some of us that have been here for awhile have given ourselves self-imposed challenges in running our airlines, to make the game more interesting. For example, running aircraft at 10-12 daily usage, seating configurations based on real-life current/historic seating configurations, etc.

 

For example, I'm running a US-based airline in one of the 1950s worlds: it's the 80s, and I just upgraded my seating config for my 727-100s from a pre-deregulation seating configuration of 12/92 (pretty close to how they were run then), to a post-deregulation config of 10/105. It's somewhat of a challenge running those on routes from Puerto Rico to Central America and some larger Caribbean destinations, but it's a lot more fun than running an aircraft up to the max once daily to each destination.

 

Especially in the worlds that start in the 1950s, it can be interesting to run some of the more-obscure aircraft: the same airline mentioned above runs NAMC YS-11s (a Japanese 60-seat turboprop built in the late 60s/early 70s that had some modest success around the world). It's not the most fuel-efficient aircraft, even for its time, but I like going for more obscure choices, again, for the added challenge.

 

I think the game can be as challenging as you want it to be, but I do agree that there is a point where you end up ignoring your airline because it's running fine. I ignored the above airline through most of the 70s, except to adjust fares.

I'm not sure, but from looking at the performance charts, I think the old numbers were in nautical miles (it's what they use in the performance charts), and they're being converted to statute miles to fix the numbers. I'm guessing Oliy can confirm or deny that.

1. Boeing 757
 

Seeing how many of my first flights were during the era of the late 90s/early 2000s US LCC tradition of having a lot of 757s fly transcontinental routes, the 757 is at the top of my list. The livery pictured is of the short lived "Red Rock" National Airlines, a quasi-LCC launched as a joint venture between some of the larger chains of Las Vegas and Reno casinos. It was launched in 1999, only to cease ops 40 months later in Nov. 2002. I've also flown ATA 757s out of MDW to LAX, LAS, and SFO/OAK(?), and an American 757 from SJO to DFW. This video of a fast, short take off, with the whine of the RB211 at full power, out of MDW makes me reminisce about a lot of family transcon trips.
 
2. Boeing 717


 
The era of the 757 rides for me ended about the time the 757 became economically unfeasible for an LCC. Future flights tended to be on AirTran, and while the legroom wasn't the best, I have many more memories of takeoffs from MDW with this other Rolls Royce-powered favorite of mine.
 
3. Lockheed L1011 Tristar
 

 
While I never did get a chance to fly on the L1011, I admire the plane for what it was: a plane with sleek lines, ahead of its time in terms of technology (technology wise, it was miles ahead of the DC-10). Between the DC-10 being pushed out ahead of the L1011 (especially the longer range versions), and the Rolls Royce debacle, the L1011 really got the short end of the stick. All things considered, the L1011 had a good career, even if the DC-10 lasted a couple of years longer on the way to retirement.
 
4. Lockheed L188 Electra
 

 
Once again, another plane I haven't really had the chance to fly. Like its later cousin the Tristar, a great plane that really didn't have much success. Airlines seemed to be reluctant to replace their DC-6s and Viscounts so soon, especially with the advent of the jet age. Early crashes put a nail in the coffin of the program, and orders didn't come in as fast as Lockheed hoped (KLM was the only European airline to order the L188). In short, I think this quote fits both of the last two planes well: "Lockheed has always built the most technologically advanced aircraft available. Unfortunately, they've never figured out how to make money doing so."
 
5. Boeing 737NG
 


Really, I have no faults with any of the 737NG models, of which I've flown on the 737-700 and -800, mostly Southwest, although I have flown on an American 738 once. I like the looks of the plane, and my rides on them have been comfortable.

If you don't use the gates you lease, you lose them after awhile.

 

EDIT: Or do you mean you're being charged 38 mil for 2 gates now?