First ignore the reports of NESASM being so bad

The people that say it is mostly have never used it or
couldn't think of good reasons. The one and only thing inaccurate about NESASM is one bad opcode is allowed (inc a). ASM6 sounds good, and should be almost the same syntax. Its mostly personal preference, nothing out of date or very inaccurate about any of the assemblers I know of. The () vs [] and banking should be the only differences in NESASM vs ASM6. If you post the error messages or some sample code then it should be pretty easy to figure out.
If you have already done some form of programming,
my unfinished tutorial may be the best. I think the version up there will get you through sprites and controller input, possibly backgrounds.
If you are starting from absolutely nothing and have more time (many weeks) you can follow along with the Nerdy Nights weekly series. It will be a couple more weeks before any useful NES code is presented.