Question 1 - Do you have one tap hole or two tap holes in your kitchen sink?
Question 2 - Do you want rubber washered (full turn) taps or ceramic disc (quarter turn) taps?If you have particularly low water pressure then I would go for traditional rubber washered taps. The rubber washer can also be easily and cheaply replaced if your tap starts to drip in the future.
Ceramic disc taps are easier to turn on and off (just quarter of a turn for on and off) so are ideal for the elderly or those with arthritis. The ceramic discs are maintenance free; so if they do start to drip then the whole tap gland needs replacing which is of course more expensive than just replacing a rubber washer and it can sometimes be difficult to source the correct size gland for your tap.
Most manufacturers these days use ceramic glands in their taps, so you will have a greater choice of these than the rubber washer types.
Question 3 - How much do you want to spend?Remember your kitchen tap is going to get lots of use. In the long run it isn't always economical to get the cheapest taps. There are lots of cheap imports these days (as with everything I suppose!) and you can get a cheap pair of pillar taps for less than £20. You will get a few years out of them before they start to drip, or the spindle gets worn, or the plastic heads split. In which case it's usually just a case of binning them and buying some new ones.
Personally, I always recommend getting a well known, quality brand like Bristan. Their taps are made in the UK (based in Tamworth) and come with a 5 year guarantee. Even if your taps fail after the five years you can give them a call and get the required spare part sent out to you. In the past I have managed to get spare parts for Bristan taps that were over 10 years old. Their advisors are very helpful.
Remember, if your taps are unbranded and made in a factory thousands of miles away the chances are you won't be able to get the required spare part. So although the cheaper taps also come with a guarantee it is difficult to see how this can be honoured.
make sure you choose taps that are suitable for your water system. If you have very low pressure (usually your hot tap) then some mono-mixers may not give you a decent flow - so check before you buy!
....and just remember, if you decide to change your own taps, the most difficult part is getting the old ones off! That's where your plumber comes in!