Completely agree with Khat17. However, I must say a few things in addition. I'll break it down...
Voice and Data Call Quality & Reliablity
FLOW's 3G network is far more complex than Digicel's (especially in the Corporate Area). FLOW's network prefers to have devices (User Equipment) sit on 3G 1900 MHz layer (where available) and only perform Inter-Frequency Handovers when the RSCP or Channel Quality is less than optimal for doing a voice call (which would make for a switch to a closer 3G 1900 MHz cell, a 3G 850 MHz cell or switch down to 2G during call setup - which itself has 2 layers which the device must select and not the network; as it would in 3G). This means that FLOW users are far more prone to dropped/failed calls especially if the Customer/User Equipment is moving at high speed.
All these variables are not present per se in Digicel's network which uses purely 850 MHz for its '4G' network. In less dense network setups (i.e. those without DC-HSDPA), they use a single 850 MHz layer. This is different from FLOW's setup of 850 MHz and 1900 MHz which gives a balance of coverage and capacity. I've only observed a second 850 MHz carrier from Digicel in Montego Bay and Kingston. FLOW has 2 3G layers in most major towns (and most annoyingly does not have DC-HSDPA in Montego Bay).
The greatest complexity can be seen in Kingston and St. Andrew where FLOW has 3 3G layers, 1 on 850 MHz and 2 on 1900 MHz (which also has Dual Carrier or Dual Cell HDSPA enabled across them). FLOW's network is optimized to have voice calls (or calls on the circuit switched domain) have the device switch up to 850 MHz for the best possible call quality and release the carrier then anchor onto 1900 MHz for packet switched activity. This setup has seen FLOW data samples on Opensignal in the Kingston Metro Area average at > 5 Mbit/s. This is unlike Digicel (which averages at < 4 Mbit/s), which has a dense network in Kingston unlike FLOW but has only 2 3G layers (2 contiguous blocks i.e. UARFCN numbers 4359 and 4384) which allows for the same speeds as FLOW's 1900 layer but added strain from Voice calls (which have to share the bandwidth) makes for a less than stellar browsing experience. This accounts for FLOW users reporting far less switch-downs to EDGE than Digicel users.
P.S. FLOW's 3G/'4G' data network is newer than Digicel's and leverages more advanced traffic management techniques than Digicel. FLOW's core network just recently concluded upgrades in November and now the company is undergoing a footprint expansion project in addition to an LTE rollout. A number of new sites are being built with a slice of GSM coverage but massive 3G and LTE capacity. FLOW also has a new co-location agreement with Digicel which will further increase the number of sites and positively impact network reliablity.