Very personal decision... I've never flown LH, even when I a had a good chance to do so... I stayed on SH because I thought that it would get me sooner to command... in the end... it took 4 years longer than I expected, and could have done both... The situation was different because it was all within the same company... I don't regret it though... flying SH for so long before the upgrade, meant that I was more experienced on type by the time I did my upgrade, and gave a lot of confidence... If I were you, I would wait for command, the sooner it comes the better... and who knows, in the future you may get a chance at a DEC position on a WB... If I am not mistaken, there was a time when Korean offered A330 DEC for A320 experienced captains and 777 for Boeing experienced CP as well... also Norwegian gave similar opportunities for experienced SH captains... Hopefully with time (and full recovery of the industry) there will be similar opportunities... but if you go for the LH FO position right now, who knows how many years you'll have to wait for the left seat... Anyways, good luck with whatever decision you make!