I think that Gatwick is a very underrated airport, flew more flights from there last year than Heathrow but mostly other airlines than BA.

Heathrow is closer to me, about 25 minutes in a taxi; Gatwick is 45 minutes by road or an hour on the train so easy to get to. Gatwick security staff make it look so easy, usually no more than 5 minutes to get through, so not really worth getting fast track most days. There was one time in 2022 where it took 45 minutes but that was an exception.

Lounge wise, if flying BA, the Business class lounge is really good, better that the two Club lounges at Heathrow T5 and T3 (I always use Cathay business lounge if flying from T3). Not had a chance to use the T5B lounge since it was refurbished.

When flying easyJet or Norwegian from Gatwick,I book into the Number 1 lounge, which is ok.