BACX because:
It's part of BA and has some of the BA benefits; strong BALPA representation, scheduling agreement, generous payment for days off working etc
The DHC8 was on borrowed time when I was there. BA's stated intention was to bin them and although they might have a temporary reprieve due operating costs in the long term BA gets rid of it's prop a/c. You will end up on jets.
Some might argue that an ideal first type is a turbp prop, then to move on to jets. Though many these days only ever fly jets from day one and they seem to do OK with it.
Sooner or later, probably when Easy go the same way as Laker, Air Europe and the rest and BA can once again crank up it's revenues, BA will loose interest in it's regional operation and incorporate it into mainline. History proves this to be the case so far: BKS, Northeast, BEA, Cambrian, Dan Air and Cityflyer. Then you'll be in to mainline and even if you hate it, you can pick up the rating for free and depart to Emirates.
Training standards; BACX's training is a combination of Brymon and BRAL training departments, mostly BRAL. Both airlines had very good training standards having trained pilots for literally decades and now BA have imposed it's standards on the BACX training machine since pilots from both airlines fly the RJ together. Even if you don't stay within the BA organisation, your first job is probably where you'll pick up the 'modus operandi' that will stick with you for the rest of your career and the standards learned there will stand you in good stead sooner or later.
BMI second choice because:
When Sir M gets sick of loosing 2m a year he'll buy Eastern and you'll be out of a job or working the same type for 10K less. History shows this also: Midland's regional SD360 and F27 work all went to what became BRAL and in turn BRAL lost work to Business Air because it's overheads were lower.
From an outsider looking at BMI, BMI mainline seems to impose what it likes on the regional operation, when and if mainline gets 'shrunk', it will be at the expense of Regional. The same is true of BACX of course, but since BACX has stronger BALPA repesentation it's less likely to happen.
Sir M has been dumping on his pilots since Derby Airways. BALPA CC might have tempered him somewhat, but he is quick to 'release' pilots when he considers it necessary.