For me the SAFEST and the most easiest to use is the cellpro from FMA. It charges and balances at the same time. It can do 2s 3s 4s at max 4amp charging. Very simple to use, just plug in your pack via the balance plugs and thats it. Plug and play and walk away. The best feature I like the most is the fuel guage.
Check out it's feature
) Adjustable current from 0.25A to 3A in ¼ amp increments. It can charge any size battery.
2) Auto Amp feature detects current of all sized packs. You can charge a 50mAh pack right after a 6400mAh pack without making any adjustments.
3) Can charge up to 24Ah packs in a single charge.
4) Low Voltage Restore repairs over discharged packs. Over discharge down to 0.5 volt per cell will be repaired to 98%.
5) Charges 1 to 4 cells individually just like a cell phone charger. That means it is impossible to start a fire.
6) Display is accurate to 10mV.
7) Cell Balance is accurate to 10mV. (That is 10/1000 of a volt!)
8) Shows Charge Amps and Amp Hours accurate to 1%.
9) Runs on 10 to 16 volt power supplies up to 5 amps.
10) Charges competitors batteries with the appropriate adapter. The will balance just like the Kokam cells.
11) Can charge thru the node connector without the Deans. This is convenient for top off charging in the aircraft.
12) Charge and control accuracy not degraded by charge lead length. Use up to six feet if you choose.
13) Can charge 1Ah and smaller packs at 3C for a 20 min to 95% charge. Full charge is 28 min!
14) Fuel gauge eliminates the guessing of battery capacity. It shows 0 to 100% and is accurate to 5%.
15) Fuel gauge instantly tells the state of the battery and allows quick 15 min fast charges in between flights.
16) All LiPos can be topped off without any danger of overcharge.
17) Can charge physically damaged packs without the danger of fire.
18) Cold weather charge mode protects batteries from over charge in the winter.
19) PC viewer software allows graphing of individual cell performance.
20) Can be directly tied with the West Mountain discharger for complete cell by cell analysis.
21) Input and output are reverse polarity protected.
22) Shows 21 different error codes to describe any problem.
23) Error codes can be reset with the press of a button.
24) Three screens show individual cell voltages, amps, amp hours, fuel gauge and charger operating mode.
25) Total plug and play without any user intervention.
26) Over temperature protection allows operation in any climate.
27) Charger runs at 90% efficiency, which means it generates very little heat.
28) The charger will handle continuous 3 amp current indefinitely up to 100 deg F ambient. Then there is a high temperature mode that drops the current down to 1.5 amps max. So, if someone tries to charge in the hot sun, the charger won’t be damaged from overheating.
29) The fuel gauge maintain 5% accuracy over the entire voltage range.
30) Charges one to four cells in series.
31) High performance microprocessor makes 14 safety checks per clock cycle even down to validating connector pin integrity.
32) Does all the above seamlessly and automatically. If you don’t care and don’t want to know, then all you need to know is that you can plug in a pack and leave the unit to do its job and never worry about fires, unbalanced cells, or swollen packs.
THIS CHARGER MAKES LI POs SAFER THAN THE MANY MILLIONS OF CELL PHONE & LAP TOP LI IONs IN THE FIELD.
Here are the reviews
http://www.rcgroups.com/forums/showthread.php?t=501252