I have the LaCrosse BC-900 battery charger. It came with 4 AA's and 4 AAA's. It's one of the best chargers out there. Point being, even if you buy Eneloops, you can still destroy them with a poor quality charger or bad charging habits. So, even if you go for the eneloops, do yourself a favor and get a good charger like the BC-900. It's not the only good one, but you can find it for around $40 and with all the extras it comes with, it's a good value and a good investment.
buying the battery packs leaves you more likely to recharge them after every time you play. Generally this shortens the life of the battery packs. Whereas with AA rechargeables, you're more likely to use them until the remote is nearly dead (or in my case when it's completely dead and cuts you off in the middle of a game).
Any rechargeable battery has a limited number of recharge cycles. So if you're putting it in a charging base after every time you use the wiimote, you're probably going to get less life out of the battery than if you run it down almost all they way before recharging. Also, quick charging tends to be harder on the batteries. Lastly, most regular chargers don't lower the current once your battery is full. Then the battery gets overcharged and heat builds up, which also tends to shorten the life.
So in short, even a great battery will seem like crap if you treat it improperly or are using a poor quality charger.