I think Nimh are a bit thin on the ground these days with lipo being so easy to use.
What matters most is looking after each cell, discharging each cell to the same voltage after use - approx .9volt - then charging on a good charger, hopefully over time your cells will remain balanced. Problems arise as the batteries become out of balance, one cell reaching a fully charged state may trip the charger to off/finished, the other cells being undercharged and under power.
If you can buy matched cells you will start off with a pack that should last, look here:
http://demonpowerproducts.co.uk/index.php?cPath=46_47
We used to carry 6 or 8 packs of side by side for a meeting, only using each pack a max of twice a day, discharge & balance between meetings. Now we have 2 lipo packs that are easypeasy, loads of power and could easy run all day on one pack topping up between heats. Dedicated lipo charger required.
I can see this sounds like an advert for lipo but you will find most use them for these reasons