All headphones have their own characteristics and the shape / size of your head will determine which are the most comfortable for you.
It's impossible to say if you will love (a) and hate (b).
Momentums have good reviews, but the reviewer does not have your ears. i.e. The reviewer may love eating lemons but you may hate them.
Then there is the question of diminishing returns. A set of £250 headphones may not have any noticeable difference in sound quality to your ears than a £100 set.
When you are paying this much for a headphone, I would suggest seeking out a good store where you can try them out first. It's far better to pay a little bit extra and make an informed and tried out choice than end up paying less mail-order for something you hate.
Also if you buy in-store, the good ones will exchange the headphones for another model after you have trialled them for a day or two.
Bose are simply overpriced like Beats Dr Dre etc. You are paying a premium for the style and name more than sound quality and comfort.
Definitely audition:
Sennheiser Momentum 2
Grado SR325e
Audio Technica ATH MSR7
Sony MDR1a
Philips Fidelio M1 mkii
AKG K550
Take your portable device with you and try different makes out. Make sure you buy from the store and not via Amazon etc. We need to support the independent retailers or we lose the customer service and ability to try these devices out when they go bust and people lose their jobs.
Good luck, hope you find what you are looking for.