I went on the gamefaqs online board which still has threads every secound or so, and made a thread saying I wanted to try out wi-fi with my FC in my sig, soo nas a refreshed some guy challanged me, I joined his room he was Lucas and I was pokemon trainer I think, we were on the ice climbers ice burg stage, which I never played on before that and it was very challenging to play on, plus I was a bit nervious, and there was definitly noticable lag and I lost, then I posted on some guys topic on gamefaqs I made a room this time, didn't take long, I was a number of diffrent characters we had about 15 matches I won slightly more, and the lag was almost non exisistent after awhile.
I think the lag gets better the more matches you have with the same person.
I had 2 friends on on another site I go to regulerly for the past 4 years that I played, it was alittle laggy sometimes. main ncharacters I use online are Falco, Fox, Lacurio, metaknight,Bowser,Snake, and PT (mainly squirtle)