It depends on what you want to do. Each has it's own characteristics and you pick based on what your target performance is. There is no 'best' type.
Suggest you Google it as there are very good articles on this on the Net. Would be tough to try and explain it fully in a few lines on a forum post. Read the well written articles as you will get to understand them properly.
LR is particularly useful as it's rolloff is -6dB at the crossover frequency and you can get closer to the drivers useable frequency . Especially in tweeters where power handling is also a criteria.
40 watts isn't a very high power rating ! But possibly response anomalies could be 'managed' more easily using a LR crossover. You do need measurement devices to implement all this properly. You can always get by and get a working system by just using published data . In that case I'd use a LR crossover.