Buying big - Although this is generally not advised, I think buying big can be good if you can afford to buy big and then follow up with adding small amounts to what you have. Buying big will help you get a good amount of bitcoins quickly.
Buying small occasionally, otherwise known by the name of dollar cost averaging - This is method that is advised for people who are not rich, and who do not have enough money to buy big. I think if you have enough money to buy big and follow up with buying small amounts, but you just decide to buy small amounts regularly, you are not doing the best for yourself.
Are there other ways apart from the one you have mentioned that we don't know because your recommendations are very funny and too plain. If you have a plan to buy Bitcoin either in large sums or small amounts, you should sit down and calculate your risk, manage it, and have a run through it before you jump into the market, review the durations you intend to hold, the time to buy, this is very crucial as it will help you as an advantage, if you get lucky and buy bitcoin at low prices, usually those times people do panic, you will enjoy that and you wouldn't have anything to fear, these supports are very rear to come by again. so, think well before you buy.