Since I have dual loyalties:
My birthplace (Caracas, Venezuela
): In 1641, the San Bernabé earthquake destroyed the little town and prompted a costly reconstruction — which would prove pointless, since the city would be destroyed again in the 1812 earthquake. However, ITTL clever minds decide to rebuild it a little more to the west — roughly around today's El Recreo parish, which is in the geographical center of the city.
With such an early POD, everything could have changed — but let's assume things follow roughly the same path. But ITTL, the city survives the 1812 earthquake with its infrastructure largely intact. As a result, the city's growth is healthier and attracts more migration from the rest of the country early on — reaching 300k inhabitants by 1900 and gaining some popularity as a gorgeous destination. Guzmán Blanco's investments in the city's renovation with a French touch certainly don't hurt, either.
Enter the oil industry and Juan Vicente Gómez. ITTL, Gómez decides that he actually likes the city. He uses most of the country's budget to invest heavily in the city during his rule. By 1936, it has more than 600k citizens and gets 70% of the national investments in infrastructure. The growth becomes unstoppable in the following decades, though — fueled by European and rural migrants. In the meantime, the Plan Rotival is followed through and increased oil revenue in the afternath of World War II allows for the construction of highways and public housing. And in 1948, the OAS is founded in the city — attracting more positive press to it.
By 1961, the Federal District — which includes its OTL territory and the eastern areas of the valley — has a population of 3 million. The traffic issues facing a city with such a fast growth are key factors behind the construction of the Caracas metro system — which is inaugurated in 1963. The metro currently has six lines, four airways and land connections to the international airport in the coast, as well as to several commuter towns within the metropolitan area.
Assuming Venezuela is able to keep its 1970s prosperity up to this day, it is likely the city (metro pop. 7.7 million) remains a major tourist destination and an important financial hub in Latin America. It is also worth noting that a lot of this growth would probably come at the expense of Maracay and Valencia, thus freeing up lots of fertile land that used to produce high quality coffee. If IOTL Venezuela produced as much coffee as Colombia by 2000, I would expect it to surpass it ITTL — which could have done wonders for the country at a time of low oil prices.
My current home (Puebla, Mexico
): In 1824, Tlaxcala is not separated from the state of Puebla. Later on, the city benefits from May 5th becoming a national holiday in Mexico, the construction of a light-rail metro system in the 1990s — as well as a Mexico City-Puebla passenger railway —, creation of the FTAA/ALCA in the 2000s with its offices in Puebla, the expansion of the airport, and the Meritorious University of Puebla (BUAP) — my alma mater — becoming an even greater university than it is today with policies more welcoming towards foreign students and faculty.
Another key factor is industrialization. Several key factories in Mexico are located here in Puebla, including the Volkswagen one that is the biggest outside of Germany. But if the city took some more — mainly from places such as Guadalajara, Guanajuato, Queretaro and the metropolitan area of Mexico City — it could have secured very important sources of income to expand its infrastructure.
Finally, better urban management could help. The city has some issues with public parking that certainly makes it difficult for people to come with their cars — a necessity in a city this big. More buses and less combis transportating people in the Cholulas and Cuatlancingo to Puebla would make a lot of people's lifes better — as well as more creative routes
such as a direct one from Cholula to the Universitary Cultural Complex, which I desperately need.
As a result of all this, Puebla becomes Mexico's second most populated metropolitan area (metro pop. 5-5.5 million) and is an even more mandatory place to visit for tourists.