The lithium packs that I'm familiar with (laptop, misc) are complicated.. and some types are potentially hazardous as far as overheating, but then almost any energy storage device is hazardous when mishandled.
Some good brands of NIMH cells with tabs are, IMO, good replacements for building battery packs for portable equipment, and although the technical aspects of charging differ between NICD and NIMH, the NICD chargers could also charge NIMH packs well.. if the charger a moderate-charging-rate delta peak sensing type (not a fast/high-rate/timer type charger).
When comparing cheap grades of different cell technologies, all bets are off, there's no point. Better grades of cells are in a separate class. The best quality/grades of cells have typically been from Japan. There are a lot of different specific cell characteristics for different grades of cells.. info from Sanyo or Panasonic give very good descriptions of their different grades.
Some sources state that NICD are better for cordless tool requirements of intermittent, moderately high drain, power. The equivalent cell size of a NIMH will provide considerably more Ah capacity, which can be a significant benefit for many applications (not primarily cordless tools).
When considering replacement of cells in older packs, one should also be considering upgrading to newer charging units. The old charger is likely to be out-of-spec and/or possibly near failure. I don't test/check out new chargers or cells unattended.. just the same habit as when charging LA lead-acid batteries.
For many of the HSMs here, replacing/bypassing the board of an existing charger probably isn't too complex, for reusing the old charger case receptacle for the existing OEM battery packs.
Some cordless power tool packs contain internal temperature protection circuits or other safety devices which shouldn't be ignored.
I've been using some universal Powerizer NIMH-NICD chargers for over a year with very good results. These are 2-wire chargers, although one or more models come with a temperature sensing lead to prevent battery pack overheating. There are some models that are AC line voltage input only, or DC input (auto/truck lighter socket cord, or AC adapter input).
Some of the MRC brand chargers have a wide variety of selectable features for different cell types and capacities.. generally limited to up to 12V maximum pack voltage, as they come supplied with 12V inputs for portable/mobile use (can also be used with 12VDC AC adapters).