I have been using the mustache style cannulas. Seem to work fine and I find them comfortable. I regularly go to 17000 ft without problem.
Three suggestions: first buy one of the cheep pulse oximeters and use it. I like to keep an oxygen saturation of greater than 85% but prefer one in the 88 to 95 range. At night you may start to loose color vision around 90% if you are old (like me), live a sea level, have lung problems or smoke (fuming is OK). Second, oxygen is expensive if you buy it from the local FBO, here it costs about $30 a fill. I made a fill manifold from three large oxygen bottles and fill my own for about $5 a fill. I split the cost with several experimental aircraft friends and we have a log of who fills and how often and split the cost of refilling tanks accordingly. Third, take the FAA high altitude training course if you can.
And fly high, fast and have fun.