Do you want something which is portable and practical, will sit on a buggy, can be carried around with sleeping child in etc (very useful) or would you prefer one which can stay in the car, and you don't have to upgrade for longer?
Budget wise you can do either for the same, for little, for more, it's not really an issue these days so it's which setup would be more convenient for you. I agree with teaandbiscuits that the combination of an infant carry type seat and then a well designed ERF seat is the best idea these days for continued safety.
Worth noting that if you decide to have another child the ones which stay in the car from birth tend to go up to about 3-4 years so if you'll have another child within that time span, they'll also need a seat of their own - whereas if you get one of each stage you can pass them down.
The pebble is an excellent seat and compatible with lots of prams so if you're looking at that it's a good choice, very popular. Around that price range, though, I'd also look at:
Britax Baby-Safe plus shr ii
Joie i-gemm
Cybex Aton 5
I would also be wary of the draw of this idea of the shared base which can work for multiple seats. It seems useful when you're looking at baby seats, but most Group 1 seats don't require a base, usually only the ones designed for these systems. The point of them is essentially to trick you, the consumer, into thinking that it's going to be most cost-effective to buy that company's next stage seat. This is not necessarily the case so I would not rely on these promises that the multi-seat base is money saving. That said, there is nothing wrong with a multi-seat base, if it seems like the right one for your infant seat, it's still worth buying, and if the next stage up seat seems like the best choice, nothing wrong with that either! But I would not let this little trick push you into thinking it's the only/best choice.