Thats really a subjective decision. Personally I prefer the Ultra Primes, half the price and weight...but your mileage will vary.
You should rent both and make a decision based on your budget and personal preferences.
The beauty of lenses as opposed to electronics (RED) is that they hold their value much longer, I purchased my Ultra Primes over 2 years ago and I bet I could sell them today for about the same price. Used standard speeds are selling today for the same and sometimes more than what they cost new years ago.



