iCloud storage price : http://support.apple.com/kb/HT5879?viewlocale=en_US&locale=en_US
So it depends if you have a good network connection for download what you need when you want (photos with iCloud, musics with spotify...) or if you want all your photos, all your iWork documents and all your stuff on your iPhone all the time.
It depends if you take a lot of videos, if you download a lot of big games from the App Store...
In fact, it depends of your money ^^
This is what I do.
I use the VLC player almost exclusively since it can play anything.
Since you want to save space and eventually download to youtube I would recommend a 2 step process.
First record it in high quality.
Then use a small app called Flv Crunch to convert "any" file format to flv type that is enormous size reduction and compatible with youtube.
It is very easy to use and control the settings.
Convert files between flv, mpeg 1/2/4, 3gp, mp3, m4a, wmv, wma, avi, mkv, aiff, and others.
Then delete the original (ok that was 3 steps :)
why do it this way?
I learned the hard way that once the event is over you are stuck with what ever quality you used to record. Thus I recommend you always record in high quality, since it is easy to reduce the file size to quality you want as end product.
For example you recorded something that needs to be magnified or altered for clarity, that would not be possible any more if recording in low quality.
About Flash Video Format:
FLV files are videos that are encoded by Adobe Flash software. They
can be played via the Adobe Flash Player, web browser plugins or one
of several third party programs. Since virtually everyone has the
player installed on their browsers, it has become the most common
online video viewing platform used on the Web today. As almost all
video sharing sites such as Youtube stream videos in Flash,
practically all browsers support and are compatible with the Flash
Video format and can play the video with ease. In addition to being an
online video viewing format, the Flash Video format is also what many
video-sharing sites convert videos to, from formats that were uploaded
by their users in something other than Flash.
This is because videos in the FLV format remain in high quality even
after compression to a smaller file size, which means that the videos
on the Web load quickly and won’t spend a lot of time using up
bandwidth.
Some notable users of the Flash Video are Youtube, Yahoo! Video, VEVO,
Hulu and Myspace among many others.
Best Answer
If you’re not a heavy user, 64GB is more than enough for what you need. Here is the size of videos in different resolution
1 minute 1080p at 30fps will be 60MB 1 minute 1080p at 60fps will be 90MB 1 minute 4K at 30fps will be 170MB 1 minute 4K at 60fps will be 400MB (Approximately) More resolution can be seen in Settings -> Camera -> Record Video
One high quality photo from my phone is a little more than 20MB.
Unless you’re filming at 4K60 all the time (for your job or something), and you don’t use big apps, 64GB is good enough for you. Otherwise go for the 256.