Both are right. This is how the Oxford dictionary entry explains the usage:
The spellings adviser and advisor are
both correct. Adviser is more common,
but advisor is also widely used,
especially in North America. Adviser
may be seen as less formal, while
advisor often suggests an official
position
These mean exactly the same thing, except when they don't. :)
From TheFreeDictionary.com
-gram
suff.
1. Something written or drawn; a record: cardiogram.
-graph
suff.
1. Something written or drawn: monograph.
This would seem to indicate that they are the same. And, in fact, if you look up pictograph and pictogram you see those words are synonyms. However, if you try to apply the logic to all words formed with the -gram/-graph suffix, you run into trouble:
ep·i·gram (p-grm)
n.
1. A short, witty poem expressing a single thought or observation.
2. A concise, clever, often paradoxical statement. See Synonyms at saying.
3. Epigrammatic discourse or expression.
ep·i·graph (p-grf)
n.
1. An inscription, as on a statue or building.
2. A motto or quotation, as at the beginning of a literary composition, setting forth a theme
So you really have to learn which is which on a case-by-case basis. Sorry.
BTW, the etymologies are different:
-graph[French -graphe, from Late Latin -graphus, from Greek -graphos, from graphein, to write; see gerbh- in Indo-European roots.]
-gram [Greek -gramma, from gramma, letter; see gerbh- in Indo-European roots. Sense 2, from telegram.]
Best Answer
From Chambers Dictionary:
I couldn't find anything on -ist. They generally all mean the same thing though and I assume the reason we have all three in English is so there is always a good aesthetic/phonetic fit for various situations.