Hi,
I asked exactly the same question before we decided on our new addition. The general view was that it doesnt matter size, age or breed wise. Saying that though, we`ve opted for the same breed, mini lop, and only two months older than our current bunny. Purely because Cocoa (the new one) is adorable and we coulnt resist!
We`re picking her up tomorrow from the RSPCA foster home where she has been since october. We found her on Rabbit Rehome (link top right of this page) and can recommend the site 100%. Within a week we have had all our questions answered and our homecheck done. Just got to go and pick the little one up now!!