Sennhesier are a fantastic audio company and I definitely recommend you give them a listen if you're in the market for new headphones.
I've never used the two headphones you've listed below and so can't comment on the different between them, I personally have a pair of CX-300 IIs that I've been using happily for over a year now and can vouch for, especially since they can be found for around $30 nowadays (Amazon has them for $27!). Personally I think you'll be be hard pressed to find a pair with better value for money.
Are SENNHEISER earbuds good?
i'm thinking of buying a SENNHEISER cx 200 or cx 280
How BIG is the difference between the CX 200 AND CX 280?