Just as there is no one most profitable poker format, there is no one most profitable poker strategy. The answer will depend on the conditions that you are playing under. Things such as the game format, your bankroll, the availability of a good bonus deal, and most importantly the other players at the table, will dictate what the optimum strategy for profit will be.
As a general guide though there are some easy guidelines. One of the most helpful things that you can do is to play in a style that is the direct opposite of the table that you are playing at. If everyone is playing tight, that is, only playing with the best cards, then should you choose to play the same way you can expect to have a long and painful game.
Conversely, at a table where most players are really loose, if you play loose too then it becomes a lottery, where the main winning factors will be luck, and to a lesser extent, the depth of your bankroll.
At a table full of maniacs, the best approach is to play tight. Playing solid cards against loose players should have a positive expectation, although the variance and the bad beats may be too much for some players to take.
Against a table full of tight players the best approach would be to play aggressively with second rate starting hands.
Make no mistake about it, neither of those approaches are guaranteed to make you money. But in general on tables of extreme playing styles your best bet is to go against the flow.
In a more balanced table, where there may be one or two loose players, and a similar number of really tight players, with most of the table being somewhere between the two extremes, a tight aggressive style of play, if it suits you, should give you the best chance of making a profit.
An element of confidence comes into play here; you need to have confidence in yourself and your abilities, and you also need to play your cards with confidence. If you are choosing your starting hands carefully then you should have confidence in the long term overall profitability of playing those hands, too.
Too many players play suited ace king with the expectation that it will be beat. The table chat often reflects these players lamenting that they always loose with AK suited, or whatever hand they had just played.
There is really no point in playing hands that you think will be beat. If that is your outlook then you should really reconsider your poker playing life completely.
Choose your starting hands based on your ability and the table you are playing against, and then play them with confidence. That is really the best style all round. It is certainly the most appropriate style that a beginner player should adopt while starting to find their feet with their hands, so to speak.