I always look for a new old stock genuine parts Fiat one, especially as the cars get older, and some dealers/retailers sell their stock off more cheaply than Fiat used to charge.
Pumps are made in China mostly, so anything with a brand name you've heard of is better than an unbranded one. Original Birth do a few parts, but anything Lucas, QH, Mehle etc. won't be too shoddy.
Mind you, I bought an unbranded jobbie for my sister's Renort once .. which was unbranded.. cost about £7, took an hour to replace (behind the wheel arch liner) and has lasted about 5 years.. so can't complain.
Ralf S.