Best Myst game for a new player?

The first one.

Really depends on how much you are into adventures/puzzles in general.

As a general guide line I'll say:

• start from the very first Myst (either the Masterpiece Edition or realMyst)
• then pick the next depending on what you liked

Little guideline based on my PERSONAL experience:

• Myst: good balance between puzzles and exploration, little plot, interesting ethical ideas.
• Riven: OMG puzzles and backtracking, little-to-no plot. The definitive Myst challenge. :)
• Exile: the Holliwood Myst: decent "movie-ish" plot with "standard" puzzles.
• Uru: weird experiment: the multiplayer part should have been central, but it was way too soon for it and never really took off. Environmental puzzles with some lateral thinking required, nice exploration, no plot.
• Revelations: a modernized Myst. Good balance between puzzles and exploration, this time with plot.
• Myst V: a Myst all about the use of "the tablet". Very forward-thinking, seeing how popular touch screens are now. A bit rudimental, easy-ish but decent puzzles, basic exploration, fair amount of plot.

All these games require patience and the will to learn. Approach them with a relaxed mind. :)

first one I played was riven, real myst was good. never played the first myst(because I played the remake realmyst) but I would assume you should start at the beginning. get myst

Of course it's better to start with the very first one. I'd recommend picking realMyst - a "3D" remake of the original.