# M/M/1 or M/M/n?

In a queuing systems with a single queue that receives $n$ poisson arrival streams with arrival rates $\lambda_1, \lambda_2, ...,\lambda_n$, and exponential service rates of $\mu_1,..., \mu_n$, we can either have a single server that have an exponential service time of $\mu_1+\mu_2+...+\mu_n$ (M/M/1)or n server with server $i$ has an exponential service time with mean $\mu_i$ (M/M/n). Both of these settings will satisfy our requirements. Which queuing system is better in terms of average delay and performance? what if the systems are M/M/1/K and M/M/n/K?