I can't speak specifically to Broward, but I'm pretty familiar with police vehicles in central Florida. As far as I can tell, there are no restrictions on the types of vehicles they can use for official purposes. Marked vehicles are fairly consistent as they are bought in fleet quantities at discount and governed by complicated contracts. The Crown Victoria was the mainstay police vehicle for many years, but went out of production. Before that happened, manufactures lobbied to get new contracts by offering small number of vehicles at a deep discount to police agencies. Chevy made a big play with the Impalas, but they turned out to be unpopular with officers. Front wheel drive, underpowered and prone to mechanical problems, they developed a bad reputation. Dodge was enjoying a resurgence at the time and made a play with the Charger and Challenger. Many of the cops I spoke with liked them but their higher cost made them less likely to be chosen. Mercury also briefly had a vehicle, the Marauder, based on the same platform as the Crown Vic, but with a great deal more power and handling/suspension improvements. Unfortunately, the combination made them prone to accidents. One agency I'm familiar with started with 12 and were down to 2 within a couple of years.

Unmarked vehicles seem to only be limited by budget concerns and that can be overcome with forfeiture. I've seen everything from mid 80's Honda beaters to brand new Escalades used as police vehicles. More commonly, you'll just see unmarked versions of the main vehicles used by the fleet, or from the same manufacturer to reduce maintenance costs and improve part compatibility.

Now, all of that is just from my practical experience from about a decade ago. I worked with several different agencies involving their vehicles and talked to many cops and fleet mechanics, but still, it's not like I'm familiar with the actual laws.

The only legal issue I'm vaguely familiar with is that when a few agencies instituted DUI units in the mid 80's without light bars, they were sued because people thought it was unfair that cop cars weren't immediately recognizable, they lost.