The main deciding factor is what you like and can afford! If you like hazelnut and can afford it, use 100% hazelnut for a classic hazelnut praline paste. If you cannot afford to buy a lot of hazelnut, then substitute some of the nuts with almonds. The more hazelnuts you have in your mix, the more hazelnut you will taste! Use almonds if you don't like hazelnuts, or if you want a more neutral tasting praline paste. You will taste almonds (obviously), but almonds have a more subtle taste compared to hazelnuts. Almonds are also cheaper and more accessible. So you can use all almonds, for an almond praline paste as well. Cashews and pecans can also be used to make praline paste. Cashew praline paste will be more creamy due to the higher fat content. Pecan praline paste will have a very distinct pecan flavor! It'll almost taste like pecan pie, but as a spread!