Okay i'm in the UK but i'm neither biased either way because i want the system that is best for both consumers and developers/publishers. Having the BBFC rate games at 15+ and 18+ is the best solution. I don't agree with them rating games at a lower level because it isn't required.
Basically, the BBFC do a more thorough investigation into the games submitted to them than PEGI do and thus this probably costs more. On the upside, this protects developers and publishers from litigation from the (stupidly uninformed) public due to lack of knowledge of game age ratings (BBFC use film ratings which are universally known whereas PEGI ratings still cause confusion in the UK public).
ELSPA sold out many years ago because they are an industry sponsored association (like the RIAA). They want what is cheapest and easiest for the developers publishers - which (debatably, because they require a separate certification process for each console version of a game - regardless of content variations or lack thereof) would be PEGI. However, this only takes into account the ease of acquiring a rating and not of being protected by law in the country that a game is sold in.
Back to why the BBFC is better for the industry than PEGI. The BBFC rate games at a lower age rating than PEGI do. Look at any game that the BBFC rates and you'll find that they rate only the most violent games at 15 and 18 age brackets. A game like Call of Juarez is a 15 game for BBFC but is 18+ for PEGI. Half Life 2 is 15 for BBFC but 16+ for PEGI. There are other examples too - especially notable where PEGI rates a game at 16+ but the BBFC does not deem a rating to be required at all.
Now, this may be considered a black mark against the BBFC because they could be said to allow more violent content to reach the consumers. Or you could take it the other way and think that PEGI actually restrict and censor more games than the BBFC do. Which some people may think is a good thing... but there is a further argument to be made:
The BBFC's rating exposes a game to a larger audience: meaning that there is a larger proportion of the population who can legally buy a game thus providing the potential to be more profitable.
Now... why do people want PEGI to be the de facto ratings body in Europe again? Remember, we recognise that a monopoly in many other areas is a bad thing... perhaps a monopoly in this area is bad too.