Best battery option for an assist bicycle

I need to get some new batteries to replace a 24v 10ah sla pack. The sla's have
worked well in terms of performance, but the lifespan has been about 80 cycles
resulting in a per ride cost of a little over one dollar per ride.

I have a pair of Schwinn Protanium Lithium batteries that appear to be
technically beyond my abilities to use confidently-- I don't want to sweat an
explosion because I am not pedaling fast enough or burn anything down while
charging.

I can go with another set of sla and keep it simple. I chose the sla for my
first pack because I was just starting out and thought I might not like the
commute, but now I am ready to do this for several years so it might be worth
investing in something better:

I am wondering about the Ping batteries at
http://www.pingbattery.com/servlet/the-6/24V-20AH-V2.5-LiFePO4/Detail

Price is higher initially, but not over the life of the battery.
Temperature range is much more realistic for my climate than Lithium.
Charge time is not mentioned.
Safety sounds like less of a concern than Lithium.
I could get more power with less weight. Is it best for battery life and
reserve capacity to get a larger capacity to avoid deep discharge?
Unlike sla's which will fit in the bicycle's factory battery case, I will have to carry these in a
bag due to their width.

I looked at Ping on e-bay last summer and it appears that Ping is making more of
an effort to provide a uniform product than before.

Is it realistic that a 24v 20ah Ping battery would last three or more years? (due to weather and other factors, I only commute about 40% of the time, so I won't hit 1000 cycles) Something better may come along in the meantime, but I don't care because the 24v 10ah is plenty for my commute even into a strong headwind-- fresh 24v 12ah sla are enough)

Are there any other good chemistry options or suppliers to explore?

Thank you to those who have assisted me in this battery quest!