Really I think this has to do with personal preference. Red box has the most recent movies and sometime a couple older movies and games. If you get one a week for one night that is about $5 a month not much less than Netflix at $8 a month streaming however Netflix also has a limited selection of newer movies and shows.
Netflix mostly has series, older movies. Occasionally a newer movies is listed on Netflix and some movies never seem to make it on Netflix no matter how old they get. Netflix does have more selection but similar to TV there may be 80% of the content you would never even consider watching or have any interest in. Redbox is good for when you want certainty that you will see what you want (although many movies are all rented out on the weekend in busy locations). Netflix is more like a replacement for TV having many many things to see but not all of it is things you want. You have to decide which aspect is more important to you.
Personally I use the 2 disc at a time from Blockbuster. I can rent movies, games and shows and they seem to have a decent selection. $15 a month for 2 discs at a time. However the shipping times have gotten slower so essentially it ends up only being 2 discs a week ( even if I send back the disc right away) It is your choice if it is worth it to you. Occasionally I will get something at Redbox and I share a subscription of Netflix with my mom so I watch it sometimes too.