When I study a game, I just look at the odds shown on the web site. To me, they really tell the story. Of course pick-3 is always going to be the game to play with the least amount of combinations. However, I don't think any lottery games are "easy," just some have more possible combinations, giving the player a less likely shot at winning with an equal amount of tickets. The less combinations possible, the better chances of winning. The more tickets you buy, your chance of winning increases even more. Our pick-4 game with odds of 1:10,000 certainly isn't easy, but there's obviously a greater chance of winning it than other games with larger jackpots.
Where did you find a 6/25 game? What is the jackpot? The odds for our 6/53 game are 1:23M so I would definitely play a 6/25 game if we had one, but I doubt if there would be a lot of rollovers and there might be multiple winners. Our Fantasy 5 game (5/36) has odds of 1:377K and isn't "easy" at all.
I think a 6 number $1 game where the odds are only 1:170,000 would be very popular, depending on the prize.