E stands for Edge, Enhanced Data rates for GSM Evolution. It is pre 3G technology and again, more likely to occur when you are in a weak signal area. You may not be able to effectively browse the internet on your device, when getting this signal.
3G (Third Generation)
3G is the third generation of the mobile network and provides adequate signal strength for browsing the internet. Most smartphone devices have the option of 3G fallback (if 4G is unavailable in your area) and 3G network towers are available in nearly every city nationwide.
H (High Speed Packet Access)
H stands for HSPA, High Speed Packet Access. HSPA (or H) is considered an advancement of the 3G networks or "version 3.5". It offers a faster network connection than the 3G network.
H+ (Evolved HSPA)
H+ stands for Evolved High Speed Packet Access. The network created before the emergence of 4G. It offers the fastest maximum speeds of all 3G networks (including 3G and H or HSPA).
LTE/4G (Fourth Generation)
Stands for fourth generation of the mobile network, and is also called LTE or Long Term Evolution. It offers the fastest maximum upload and download speeds of any network. For a network to consider itself 4G, it must meet the standards of the ITU or International Telecommunications Union.
Keep in mind, many H+ (HSPA+) networks mimic the speeds of 4G (or LTE), but because they do not meet the ITU requirements, they do not get the title of “LTE”.