There used to be 3 models sold:

• 64: LCD screen, Slowest storage, no anti-reflective glass, regular battery
• 256: LCD screen, Fast storage, no anti-reflective glass, regular battery
• 512: LCD screen, Fast storage, anti-reflective glass, regular battery

If your region still has the 64 or the 512 for sell they'll be highly discounted. The 64 I think it's not worth it, because it's too small disk size, the 512 is what I have and I'm very happy with it.

Currently the three models sold are:

• 256: LCD screen, Fast storage, no anti-reflective glass, regular battery
• 512: OLED screen, Fast storage, no anti-reflective glass, large battery
• 1TB: OLED screen, Fast storage, anti-reflective glass, large battery

If you don't care about the anti reflective glass the new 512 is very tempting, 512 is more than enough and you can always put SD cards for extra games. Personally I would go for the highest one, larger internal storage is always preferable to SD cards, the anti-reflective glass is worth it and if you're going to be travelling a lot the large battery is surely worth it. If the price is too high, the 512 is very close.

As for the usage afterwards, my deck has seen lots of usage, the biggest problem I have with the switch is very limited game catalogue (not that they don't offer enough games, but I have very few because they're really expensive). If you like gaming, the deck is great because it allows you to squeeze 5min gaming sessions whenever you have free time, which a PC doesn't because it takes 5min to open steam, open the game, load your save, etc, whereas on the deck you unlock it and you're back where you stopped in a matter of seconds.