I own all the BFG fleets + extras except for the Tyranids and Tau which are the only GW space fleets I didn't approve of in terms of sculpting quality and design so I didn't buy them.
The rest are different and cool.
I also own space fleets from other manufacturers.
I don't play BFG any more, it's ok, but it's not for me.
I gave all my rulebooks and counters etc to some young guys who were looking to get into it but didn't have a lot of money to get started.
I do use the ships though, because they look good, in two other space fleet systems that I play.
Starmada is an excellent system from Majestic 12 games, really quite complex in it's options and expansions but still very good for all that. MJ12 are a very conscientious gaming company. The system is a little demanding (indepth) to learn but once you have it down it's a very good game but some of the variations (movement for instance) they offer the players are better than others.
You can use all your BFG toys for Starmada.
You can create your own ships in Starmada.
Full Thrust takes the trophy for being my favourite game in the space fleet battle genre.
Ground Zero Game's legendary space fleet game has the record for the most decorated sci fi space game in the history of sci fi space games.
It has a global following.
Full Thrust has won best sci fi miniature game awards since the mid to late 90's and it has evolved slowly over that time.
It maintains complete flexibility for the customer/player and it keeps the gameplay moving at a good clip once you have the rules down.
The more recent GZG fleets are also excellent models. (The earlier were pretty ugly)
You can use all your BFG toys for Full Thrust.
I do.
You can create your own ships in Full Thrust.
Spartan Games have a new space fleet based game due out soonish and it looks like it could work really well if it utilises the same engine as the excellent design used for Uncharted Seas.
Some of the models for this game are on the Spartan Games website and their space ships look very sexy indeed.
Babylon 5 is a fun space fleet game but a common complaint is that the different fleets could be better balanced.