I'm not sure about the term "Petrol". The clear stuff should be labeled Blanco (white) or Plata (silver). Usually un-aged. Reposado is aged a bit in barrels and Aņejo is aged the longest. I like Aņejos for sipping although any age can be decent to sip if it's good quality. I've never been much for shooting it.
Like a lot of booze categories over the last decade or so, Tequila became popular and trendy and exploded with tons of brands. I'm not too current with what's good out of the newer ones.
I've always thought Don Julio was a good, safe one if you just wanted to grab a bottle without thinking. Classic, good, not cheap but not crazy expensive. Kind of like Macallan Scotch, always a nice standby. If you want to spend some money, Don Julio 1942 is really nice, but definitely spendy.
Other "normal" brands (common in stores, been around a while, not boutique brands or too expensive) that I like would be Milagro, Centenario, Corralejo and Herradura. I've never understood the appeal of Patron. To me it's always seemed overpriced, not horrible but not great, way too many other ones to try with more character and that are less expensive. Get 100% agave. The good ones will be anyway and nowadays there are plenty of cheap ones that are 100% as well, so no need to bother with the lesser stuff.
Like Matt said, mezcal is worth a look as well. It was always known as the cheap crap with the worm in it in the US but, like so many things, there's more to it than that. Tequila can only be made from blue agave, but mexcal can be made from a bunch of different varieties. So there's a big range of flavors you can get from that category. Off the top of my head, I only know one brand name, and it also depends where you're located as to what's available. The one I know is Del Maguey. There are several different ones that they do and a crazy range of flavors - sweet, smoky, mild, strong, etc. They're made in small villages and done very traditionally, donkeys turning the millstone and stuff. Look them up and you'll see the different flavor profiles from them. Many more mezcals to explore though, I'm just blank on any specific names.......
One more thing to check out, if you can find it, is Sotol. Similar to mezcal and Tequila, kind of like a rougher cousin. Made from a different plant. Interesting stuff, more from Northern Mexico. It was known as a kind of moonshine where if you were in little out of the way bars in Mexico, each bar might have their own, different version of it made by someone locally. I've known guys in Texas who lived and traveled in the border areas and that's how they discovered it, in the tiny village cantina places. Sometimes firewater, sometimes like horsepiss, but every once in a while you'd get lucky and uncover a gem.
I don't think Sotol took off like Mezcal, but quite a few years ago there were a couple of "proper" brands that came to the US. Very cheap compared to Tequila and was a pleasant surprise with how nice it was to drink. Bold and definitely had some flavor but smooth enough to sip. I haven't looked for that in a while so I'm not sure if it ever took off or if it disappeared.
Hope that wasn't too wordy.........