Ford explorer would be sick as i saw many dashcam pursuits of many US PDs that use it, besides it looks very nice with Police markings and ELS.
It's a pity that TDM doesnt have many modern SUVs as any of theese would look and perhaps perform better:
Ford Explorer as u mentioned
Chevy Tahoe could be instead of Escalade
BMW X3 or X5 would be an EU equivalent of the porche, as PLPD is more like GB police than US
And apart from PD vechicles I would love to see a G-class, as its a very popular gang/mafia car and also looks sick.
The SUVs might be harder to model, but they are very popular cars in general. The second thing might be balance as the SUVs has to be heavier than other cars and It may influence civ gameplay, and maybe people would prefer buying them over light sportcars.