if your ambition is to play in cash ring games, then the best practice will be cash ring games...the problem is, esp. if your playing no limit, that you can lose all your money very quickly...with an SnG the most you can lose is your buy-in, so typically you get more hands for your money. Also as you progress you get to see a greater varity of situations (i.e. 10 handed game, 9 handed game, 8 handed...all the ways to heads up, and high blinds and low blinds) and learn how to adjust your game accordingly...

if your going to play limit ring games, then i wouldn't bother with SnGs, go straight to the tables, there aren't that many limit SnGs anyway. But if your planing on playing no limit ring games then i think some cheap SnGs (many sites have them for less than $5, some less than $1) could help you get a feel for the game, as long as your aware of the differences between tourney and ring game play (e.g. ring games are generally tighter, because there are no escalating blinds forcing the action).

BTW: when you say 5/10, I assume you mean $0.05/$0.10 not $5/$10...you don't want to learn to play on the $5/10 table

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I love him who is ashamed when the dice fall in his favour and who then asks: Am I then a cheat? for he wants to perish.