I've been a junkie in New England and in SoCal so I've seen both sides of the coin.
In New England, we get Columbian powder heroin. It's light tannish and If you've got a good Dominican connect in the northeast, you can get solid rocks of fine tan powder sold by weight. If you go towards New York, or towards western Massachusetts and Vermont, you start finding the branded stamp bags that vary in quality but never disappoint. The best straight heroin (without fentanyl) I've ever done has been from New York and Connecticut and 2 bags laid me out despite my tolerance. East Coast dope, especially NYC, Baltimore, and Philly dope, is of the finest quality but is also relatively expensive.
Heroin in the west is a totally different scene, with the Mexican tar. I just got back from a bender in San Diego and Tucson. Junkies out there smoke crystal and shoot tar, junkies out east smoke crack and shoot powder. A drug habit is FAR more affordable in the Southwest. Tar is a cruder, dirtier high, but it's fucking cheap. Starting out, you can get 4 good shots out of a 20 dollar ball, as long as you're getting good shit (only buy from Hispanics!). Being close to the port of entry, the quality can be very good and the price is right. You can maintain a habit at 20 bucks a day which is impossible in the northeast. Watcj out though, shooting tar will absolutely destroy your veins. Its basically just refined plant matter and is horrible for your body when injected. It also contains no actual diacetylmorphine - mostly 6-MAM and assorted opiates, but the rush hits you just as hard. However, the high itself is very sedating, itchy, and noddy, which some people like. I find east coast powder to have a more euphoric, uplifting, clean quality.
By far the most potent dope I've tried has been that grey shit laced with fentanyl that has been dropping white suburban kids left and right in New England. Only got to try it once and i was so excited my blood pressure was through the roof and couldnt find a good vein. Ended up totally missing the vein but before i could even get angry it hit me, hard. I could barely even stand up, and I did half of what I'd normally do. It cut right through 80 mg of methadone. The high wasnt quite as warm and euphoric but was fucking powerful.