There is no standard, gold, silver, or lead.
Sadly there is no
disassemblers section on the wiki, so it's very difficult to give you a list of all the 6502 disassemblers available (I'll start working on that as we speak). There are several, but none are "magical" in the sense of "magically figure everything out for me!"
The 6502 disassemblers I've used in recent days are da65 (part of the cc65 suite -- this is an advanced suite and you will probably find yourself spending a lot of time just learning how to use this suite, esp. if you plan on reassembling the disassembled results),
dasm (by Matt Dillon), and
disasm6 (by Frantik here on the forum; this is an executable version of a PHP script). You'll need to get familiar with the .NES file format (16-byte header) since the former two disassemblers do not understand the file format/will try to disassemble the header.
You're going to almost certainly need to get familiar with emulators that have debuggers (ex. FCEUX, Nintendulator, etc.) as well, in case there's something you need to sift through in real-time (likelihood of this is high). You'll probably spend more time in this than in an actual disassembly.
Do you have familiarity with 6502 at all (re: "...what I want to do is disassemble the ROM, but I have no experience with this type of thing...")? If not, start there.
Do you have familiarity with NES registers and the PPU (particularly nametables, pattern table, attribute table, and palette)? If not, start there too.
Many romhackers end up finding someone (usually on romhacking.net's forum) that is already familiar with these and opts to help out with the project.