I think which console is best to collect for is a very personal thing, based on your own gaming habits & income level.
I think, for me personally, I'd pick the Saturn. I didn't grow up with it, but I wanted it way back when I was just 13. Coupling that with the higher cost of the games (meaning I only pick up one or two a year), makes Saturn acquisitions special. It simultaneously appeals to my desire to try something new, while encouraging a sense of faux nostalgia & appealing to the kid in me who never got her Saturn back in the day. It's a great way to rekindle that childlike wonder for games from before I had such a big collection. Plus- since the games are so pricey, the collection is far more curated, so it's overall higher quality & more bragworthy than the rest of my stuff.
If I were trying to encourage a new collector, I'd probably point them toward the PS2/3 and handhelds right now- the games and systems both are fairly plentiful and cheap, with lots of great titles to find- they're fine places for someone to try this whole thing out without putting in too much money. The Wii and 360 are close seconds. The Wii gets knocked a bit for the large amount of shovelware to dig through, and the 360 has enough console issues to put me off recommending it to someone who doesn't know what to look out for. Pre-NES systems can be good for the tinker-minded types, since doing home repair & mods isn't out of the norm- and they're dirt cheap. The games decidedly don't appeal to many people these days though.
For someone who insists on picking up the popular systems right at the start- your NES/SNES stuff- I'd really try to push them to emulation. It's a far more expensive set of the market to get into, & I'd rather they not put in a huge money sink to find out it's just not their thing.