Can only talk from a Nikon view but... 1.8 is just over £110, 1.4 is around £270. Is the 1.4 more than twice as good as the 1.8 - probably not. What would be the 1st lens I would buy if all my kit broke - 1.4!!
The 1.4 is a lovely lens, although I rarely use 1.4. Occasionally 2.0, 2.8 and mainly 4.0 but I just feel that the 1.4 is sharper overall. The difference is certainly not like comparing a kit lens to a 2.8 lens but I do feel the 1.4 is better.
Cant go wrong with either. If you have the money then get the 1.4, although (assume Sony prices are similar to Nikon) you could get a 1,8 and flash for the same as a 1.4 on its own, so depends what you already have/need.