msm, I had the same thoughts about two years ago when I achieved GfL and, because I had just retired and stopped travelling very much, I had no chance of getting GGLfL.

There are some good suggestions above, but some of my key thoughts were:

One of my regular routes is MAD > ABZ. LH stopped flying to ABZ; avoiding AF and the CDG zoo was a no-brainer. KLM via Schiphol is no picnic either. The T5 transfer experience is pretty straightforward, so I keep going BA or IB.

As I now fly on my own Euro, I usually book Y and using another airline or alliance would not give me the benefits of fast track, lounge access, etc.

When researching travel I always check pricing. Sometimes BA/IB win, sometimes they don't. Last year I used AF/KL for a USA trip - notwithstanding my comments above - they simply beat BA on price. I was looking for a trip in J to Asia next year and the ME3 all came in around the same - then BA came in 20% less, so I booked with BA.

Keep in mind that if you book with BA in CW, you might (might!) be in line for an upgrade to F - when travelling on business my success rate was probably 33%.

I think a little bit of loyalty to BA can pay off - I don't know how it all works in the background, but I've had a few IROPS recently and they fixed it very quickly and smoothly.

Horses for courses, of course.

Whatever you do, enjoy!

(A pedant note for some: In BA it is called 'Gold for LIfe', not Lifetime Gold.)