I would prefer lie flat to avoid oxygen desaturation issue and because they're supposed to be a better position for babies under 6 months.
We are looking at Britax safe sleeper, also aprica euroturn and jane. I think there is one called a mutsy.
I've heard that previously carrycots were not considered as safe as rear facing. But
Which? rates the new britax carrycot highly including on safety and it's won other awards so i wonder if that's turned a corner. I've also only heard good things about the aprica which tho expensive is lie flat and converts to last til 4yrs.