I think the question itself is flawed, as it implies employing a risky min/max strategy.  Rather than going all in on one or the other we should be asking ourselves what kind of spread we want. 

Steem is more decentralized than Steemleo, making it the safer bet.  Steem is also guaranteed to have more development due to the constant work Steemit Inc. does for the protocol.  

That being said, it only takes 6k Leo to become a whale at this point.  It's a lot easier to get in now and own a very large percentage of the network. 

Leo piggybacks off of Steem, so everyone that uses Leo must have enough Steem to even transact on the blockchain.  At the moment this doesn't matter much because the 20 or so Steem coins required to transact will only set one back less than $5 at the moment. 

Leo is a highly speculative asset.  Unlike Steem, Leo currently has no advantage to holding in terms of on-chain governance. Going forward I believe this will be one of the make or break attributes of these communities.  There must be legitimate reasons to stake coins other than blind speculation. 

Leo is also much more centralized and currently controlled by a single entity.  This isn't necessarily bad, because the SteemEngine team can do highly experimental functions and smart contracts long before the Steem team can ever implement them.   We can think of SteemEngine as a prototyping testnet for SMT protocol. 

Do you like one community more than the other?  
Do you see yourself more active on Steem or Leo? 

# Conclusion
It looks like you're clearly interested in both, so invest in both.  
* 1/3 Steem to 2/3 Leo is the risky spread.
* 50/50 would be like an even partnership. 
* 2/3 Steem to 1/3 Leo is the safe play. 

I've learned the hard way over the last two years that making the safe play is always the best idea because volatility is so high.  When we make safe plays to lower that volatility we are much more likely to come out on top.  To be fair, I'm not very good at taking my own advice.