I've done both, stayed in PERPIGNAN and Spain. My personal apinion is to stay in Spain. Definitely cheaper, more nightlife. Only just over an hour transfer.

Done both
Basically both are very good
The Spain option like Nidger says involves the transfer in/out on the day of the game buy some real good transfer deals with CST/Foti
The experience is more of a holiday feel IMO with the game as a Gameday experience
I've usually found the flights to be on average a bit more expensive that time of year into Girona, but not much, although currently you'd be looking about 250/300 return at least
But the Beer is deffo cheaper

The Perpignan option, we did slightly differently this year
We flew in to Beziers and had a night round there and it was very good
Flights were cheaper (about 150) but Beer a bit more expensive (on average I'd say £6 a pint)
We then took train to Perpignan following day(and picked up some scotish friends at Narbone who had flown into Carcassone day before). Took about an hour in train for €10
We then had an evening in Canet on the bus for €2, which is a beachside location, very nice etc. About 40mins on the bus and has a bit of a Spanish feel to it like going to lloret etc. That is also another option.
Stopped in Perpignan for 3 days then a night back in Bezier before flight home
We stopped in Ibis Budget hotels and although very basic was OK for 3 of us as we basically only slept in the room.
The room was about £30 pp per night inc taxes

This year we've already booked flights out to carcassonne for the Friday morning (only paid £40) just to experience something different, beziers is also £40 going out, not worked out getting home yet but the Wednesday after return is cheap as well

Would probably end up going to Perpignan for Friday/Saturday and then go somewhere like Canet Sunday/Monday and then a trip into Beziers Tuesday for flight home Wednesday

I find the Perpignan/France bit has more of a stag/lads do feel
With a lot of the families doing the Spain and transfer in on day bit.

Perpignan used to be extremely lively either side of game day but I found it pretty quiet this year. Due to several of us travelling that wasn’t a problem however, if you are travelling on your own, or as a couple, I would suggest going to Spain. Lloret will be bouncing in August and there will be many other fans making the trip that you can join in the bars. Personally, I prefer to stay at Santa Susana. Consider flying into Barcelona, there is a good rail connection to SS but, as Jukes has said you can also get reasonably priced transfers with Foti. I would suggest booking your transfer to the game with the same provider as they can also provide you with a match day ticket in the Wigan end.

I forgot to say El Pub is a good rugby league bar in Lloret and the Drunken Duck in Santa Susanna is worth a visit.

Thanks guys, plenty to think about there.