Well it depends on your budget and how many eggs you want to hatch.
The rcoms and brinseas are all very good machines and these are generally priced around the £200 - £275 mark, you can pick them up cheaper on ebay without all the auto functions eg: basic Octagon 20 eco with turner priced @ £170 or the top of the range Octagon 20 Ex Advance with pump @ £250. Rcom 20s are a bit more expensive ranging from £299 to the pro version at around £399. You can purchase the King Suro the basic Rcoms model for upwards of £120 which are perfectly adequate.
At the top end price of the Rcom and Brinseas though you start entering into the league of quality cabinet incubators e.g. the MS machines which have a larger capacity for hatching eggs starting at 35 hen eggs. The cabinets are simple machines with high build quality and insulation. The bigger size can absorb slight variations in temp and humidity so are more forgiving than the plastic hulled incubators, you can also "trickle" hatch, meaning topping up with a fresh set, whilst not disturbing the already incubating eggs. A separate "hatching tray is supplied. The MS incubators start at around £300 for a 35 semi automatic.