Newbie question - Using a microcontroller with analogue input

Firstly, I must state that I have never programmed a microcontroller
before, although I'm used to designing CMOS logic circuits and
programming other forms of instrumentation. Also, I feel that function
block software would be more appealing to me than ladder logic.

I want to purchase a "smart relay" or microcontroller that is 24VDC
powered and that can accept at least one analogue process input
(4-20maDC preferably, but 0-10VDC will do).

The function of the controller should be as follows:

The input signal is compared against a high setpoint and a low
setpoint. If the signal is below the low setpoint, a relay output is
energised. If the signal is between the high and low setpoints, the
relay is de-energised. If the signal is above the high setpoint, the
relay output is energised.

I would like also like to delay the relay energising by an adjustable
amount (0-5 seconds). I don't want the relay to respond to short term
input changes.

Once programmed, I would like to be able to adjust the high and low
setpoint values and the time delay by means of pushbuttons and LCD
display on the front of the controller.

I've looked at a few makes - Siemens "Logo", IDEC "SmartRelay",
Mitsubishi "Alpha", Telemecanique "Zelio" (I'm based in Europe).

Could anyone kindly comment, please, on their experience, good or bad,
with the ADC stability on the analogue input to the above controllers.
Does one particular make of controller lend itself to my application?

I've got to go through the learning curve of the programming software
and would appreciate some advice on which is the best controller to
plump for.

Many thanks.